IPS Julian Satran Internet Draft Daniel Smith Document: draft-ietf-ips-iSCSI-06.txt Kalman Meth Category: standards-track Ofer Biran IBM Costa Sapuntzakis Cisco Systems Matt Wakeley Agilent Technologies Luciano Dalle Ore Quantum Paul Von Stamwitz Adaptec Randy Haagens Mallikarjun Chadalapaka Hewlett-Packard Co. Efri Zeidner SANGate Yaron Klein SANRAD iSCSI Julian Satran Standards-Track, Expire November 2001 1 iSCSI April 19, 2001 Status of this Memo This document is an Internet-Draft and fully conforms to all provisions of Section 10 of RFC2026 [1]. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or made obsolete by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract The Small Computer Systems Interface (SCSI) is a popular family of protocols for communicating with I/O devices, especially storage devices. This memo describes a transport protocol for SCSI that operates on top of TCP. The iSCSI protocol aims to be fully compliant with the requirements laid out in the SCSI Architecture Model - 2 [SAM2] document. Acknowledgements In addition to the authors, a large group of people contributed to this work through their review, comments and valuable insights. We are grateful to all of them. We are especially grateful to those who found the time and patience to participate in our weekly phone conferences and intermediate meetings in Almaden and Haifa, thus helping to shape this document: Jim Hafner, John Hufferd, Prasenjit Sarkar, Meir Toledano, John Dowdy, Steve Legg, Alain Azagury (IBM), Dave Nagle (CMU), David Black (EMC), John Matze (Veritas), Mark Bakke, Steve DeGroote, Mark Shrandt (NuSpeed), Gabi Hecht (Gadzoox), Robert Snively (Brocade), Nelson Nachum (StorAge), Uri Elzur (Intel). Many more helped clean up and improve this document within the IPS working group. We are especially grateful to David Robinson and Raghavendra Rao (Sun), Charles Monia, Joshua Tseng (Nishan), Somesh Gupta, Michael Krause, Pierre Labat, Santosh Rao (HP), Stephen Bailey (Sandburst), Robert Elliott (Compaq), Steve Senum (CISCO), Barry Reinhold (Trebia Networks). The recovery chapter was enhanced with Satran, J. Standards-Track, Expire November 2001 2 iSCSI April 19, 2001 help from Stephen Bailey (Sandburst), Somesh Gupta (HP), Venkat Rangan (RhapsodyNetworks) and Doug Otis (Sanlight). Last, but not least, thanks to Ralph Weber for keeping us in line with T10 (SCSI) standardization. We would like to thank Steve Hetzler for his unwavering support and for coming up with such a good name for the protocol, Micky Rodeh, Jai Menon, Clod Barrera and Andy Bechtolsheim for helping this work happen. At the time of the writing, this document has to be considered in conjunction with the "Naming & Discovery" and the "Boot" documents. The "Naming & Discovery" is authored by: Mark Bakke (Cisco), Joe Czap, Jim Hafner, John Hufferd, Kaladhar Voruganti (IBM), Howard Hall (Pirus), Jack Harwood (EMC), Yaron Klein (SANRAD), Lawrence Lamers (San Valley Systems), Todd Sperry (Adaptec) and Joshua Tseng (Nishan). The "Boot" is authored by: Prasenjit Sarkar (IBM), Duncan Missimer (HP) and Costa Sapuntzakis (CISCO). We are grateful to all of them for their good work and for helping us correlate this document with the ones they produced. Conventions used in this document In examples, "I->" and "T->" indicate iSCSI PDUs sent by the initiator and target respectively. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119. Satran, J. Standards-Track, Expire November 2001 3 iSCSI April 19, 2001 Table of Contents Status of this Memo...................................................2 Abstract..............................................................2 Acknowledgements......................................................2 Conventions used in this document.....................................3 1. Overview...........................................................9 1.1 SCSI Concepts...................................................9 1.2 iSCSI Concepts and Functional Overview.........................10 1.2.1 Layers and Sessions.........................................10 1.2.2 Ordering and iSCSI Numbering................................11 1.2.2.1 Command Numbering and Acknowledging......................11 1.2.2.2 Response/Status Numbering and Acknowledging..............13 1.2.2.3 Data Sequencing..........................................13 1.2.3 iSCSI Login.................................................14 1.2.4 Text Mode Negotiation.......................................15 1.2.5 iSCSI Full Feature Phase....................................16 1.2.6 iSCSI Connection Termination................................17 1.2.7 Naming and Addressing.......................................18 1.2.8 Message Synchronization and Steering........................21 1.2.8.1 Rationale................................................21 1.2.8.2 Synch and Steering Functional Model......................21 1.2.8.3 Synch and Steering and Other Encapsulation Layers........25 1.2.8.4 Synch/Steering and iSCSI PDU Size........................25 2. iSCSI PDU Formats.................................................27 2.1 iSCSI PDU Length and Padding...................................27 2.2 PDU Template, Header and Opcodes...............................27 2.2.1 Header Digest and Data Digest...............................28 2.2.2 Basic Header Segment (BHS)..................................28 2.2.2.1 X........................................................29 2.2.2.2 I........................................................29 2.2.2.3 Opcode...................................................29 2.2.2.4 Opcode-specific Fields...................................30 2.2.2.5 TotalAHSLength...........................................30 2.2.2.6 DataSegmentLength........................................30 2.2.2.7 LUN......................................................31 2.2.2.8 Initiator Task Tag.......................................31 2.2.3 Additional Header Segment...................................31 2.2.3.1 AHSType..................................................31 2.2.3.2 AHSLength................................................31 2.2.4 Extended CDB Additional Header Segment......................32 2.2.5 Bi-directional Expected Read-Data Length Additional Header Segment...........................................................32 2.3 SCSI Command...................................................33 2.3.1 Flags and Task Attributes...................................33 Satran, J. Standards-Track, Expire November 2001 4 iSCSI April 19, 2001 2.3.2 CRN.........................................................34 2.3.3 CmdSN - Command Sequence Number.............................34 2.3.4 ExpStatSN/ExpDataSN - Expected Status Sequence Number.......34 2.3.5 Expected Data Transfer Length...............................34 2.3.6 CDB - SCSI Command Descriptor Block.........................35 2.3.7 Command-Data Data Segment...................................35 2.4 SCSI Response..................................................36 2.4.1 Byte 1 - Flags..............................................36 2.4.2 Status/Response.............................................37 2.4.3 Basic Residual Count........................................37 2.4.4 Bidi-Read Residual Count....................................37 2.4.5 Sense or Response Data Segment..............................38 2.4.6 ExpDataSN...................................................38 2.4.7 R2TExpDataSN................................................38 2.4.8 StatSN - Status Sequence Number.............................38 2.4.9 ExpCmdSN - Next Expected CmdSN from this Initiator..........38 2.4.10 MaxCmdSN - Maximum CmdSN Acceptable from this Initiator....39 2.5 SCSI Task Management Command...................................40 2.5.1 Function....................................................40 2.5.2 Referenced Task Tag.........................................41 2.6 SCSI Task Management Response..................................42 2.6.1 Referenced Task Tag.........................................43 2.7 SCSI Data-out & SCSI Data-in...................................44 2.7.1 F (Final) Bit...............................................45 2.7.2 Target Transfer Tag.........................................46 2.7.3 StatSN......................................................46 2.7.4 DataSN......................................................46 2.7.5 Buffer Offset...............................................46 2.7.6 DataSegmentLength...........................................47 2.7.7 Flags.......................................................47 2.8 Text Command...................................................48 2.8.1 F (Final) Bit...............................................48 2.8.2 Initiator Task Tag..........................................48 2.8.3 Text........................................................49 2.9 Text Response..................................................50 2.9.1 F (Final) Bit...............................................50 2.9.2 Initiator Task Tag..........................................51 2.9.3 Text Response Data..........................................51 2.10 Login Command.................................................52 2.10.1 X - Restart................................................52 2.10.2 F (Final) Bit..............................................53 2.10.3 Version-max................................................53 2.10.4 Version-min................................................53 2.10.5 CID........................................................53 2.10.6 ISID.......................................................53 2.10.7 CmdSN......................................................53 Satran, J. Standards-Track, Expire November 2001 5 iSCSI April 19, 2001 2.10.8 ExpStatSN..................................................53 2.10.9 Login Parameters...........................................53 2.11 Login Response................................................55 2.11.1 Version-max................................................55 2.11.2 Version-active/lowest......................................55 2.11.3 InitStatSN.................................................56 2.11.4 Status-Class and Status-Detail.............................56 2.11.5 TSID.......................................................58 2.11.6 F (Final) bit..............................................58 2.12 NOP-Out.......................................................60 2.12.1 P (Ping) Bit...............................................61 2.12.2 Initiator Task Tag.........................................61 2.12.3 Target Transfer Tag........................................61 2.12.4 Ping Data..................................................61 2.13 NOP-In........................................................62 2.13.1 P bit......................................................62 2.13.2 Target Transfer Tag........................................63 2.13.3 LUN........................................................63 2.14 Logout Command................................................64 2.14.1 CID........................................................64 2.14.2 ExpStatSN..................................................65 2.14.3 Reason Code................................................65 2.15 Logout Response...............................................66 2.15.1 Response...................................................66 2.16 SNACK Request.................................................67 2.16.1 S..........................................................67 2.16.2 AddRuns....................................................67 2.16.3 BegRun.....................................................68 2.16.4 RunLength..................................................68 2.16.5 ExpStatSN/ExpDataSN........................................68 2.16.6 Additional Runs............................................68 2.17 Ready To Transfer (R2T).......................................69 2.17.1 DataSN.....................................................70 2.17.2 StatSN.....................................................70 2.17.3 Desired Data Transfer Length and Buffer Offset.............70 2.17.4 Target Transfer Tag........................................70 2.18 Asynchronous Message..........................................71 2.18.1 iSCSI Event................................................72 2.18.2 SCSI Event.................................................72 2.19 Third Party Commands..........................................73 2.20 Reject........................................................74 2.20.1 Reason.....................................................74 2.20.2 First Bad Byte.............................................75 3. SCSI Mode Parameters for iSCSI....................................76 3.1 SCSI Disconnect-Reconnect Mode Page use in iSCSI...............76 3.1.1 MaximumBurstSize Field (16 bit).............................76 Satran, J. Standards-Track, Expire November 2001 6 iSCSI April 19, 2001 3.1.2 E - Enable Modify Data Pointers Bit (EMDP)..................76 3.1.3 FirstBurstSize Field (16 bit)...............................76 3.1.4 Other Fields................................................77 3.2 iSCSI Logical Unit Control Mode Page...........................77 3.2.1 Enable CRN (C)..............................................78 3.3 iSCSI Port Mode Page...........................................78 3.3.1 Protocol Identifier (iSCSI).................................79 3.3.2 Enable ACA (A)..............................................79 3.3.3 LogoutLoginMinTime..........................................79 3.3.4 LogoutLoginMaxTime..........................................79 4. Login Phase.......................................................80 4.1 Login Phase Start..............................................81 4.2 iSCSI Security and Integrity Negotiation.......................82 4.3 Operational Parameter Negotiation During the Login Phase.......84 5. Operational Parameter Negotiation Outside the Login Phase.........85 6. iSCSI Error Handling and Recovery.................................86 6.1 Format Errors..................................................86 6.2 Digest Errors..................................................86 6.3 Sequence Errors................................................87 6.4 Protocol Errors................................................87 6.5 Connection Failure.............................................87 6.6 Session Errors.................................................88 6.7 Recovery Levels................................................88 6.7.1 Recovery Within-task........................................89 6.7.2 Recovery Within-connection..................................90 6.7.3 Recovery Within-session.....................................91 6.7.4 Negotiation Recovery........................................91 6.7.5 Session Recovery............................................91 7. Notes to Implementers.............................................93 7.1 Multiple Network Adapters......................................93 7.2 Autosense and Auto Contingent Allegiance (ACA).................93 7.3 Task Management Commands and Immediate Delivery................93 Appendix A...........................................................96 8. Security Considerations...........................................97 8.1 iSCSI Security Protection Modes................................97 8.1.1 No Security.................................................97 8.1.2 Initiator-Target Authentication.............................97 8.1.3 Data Integrity and Authentication...........................97 8.1.4 Encryption..................................................98 9. IANA Considerations...............................................99 10. References and Bibliography.....................................100 11. Author's Addresses..............................................102 Appendix B. iSCSI Security and Integrity............................104 01 Security Keys and Values.......................................104 02 Authentication.................................................106 03 Login Phase Examples...........................................109 Satran, J. Standards-Track, Expire November 2001 7 iSCSI April 19, 2001 Appendix C. Examples................................................118 04 Read Operation Example.........................................118 05 Write Operation Example........................................119 Appendix D. Synch and Steering with Fixed Interval Markers..........120 06 Markers At Fixed Intervals.....................................121 07 Initial Marker-less Interval...................................121 Appendix E. Login/Text Miscellaneous Keys...........................122 08 MaxConnections.................................................122 09 TargetName.....................................................122 10 InitiatorName..................................................123 11 TargetAlias....................................................123 12 InitiatorAlias.................................................124 13 TargetAddress..................................................124 14 SendTargets....................................................125 15 AccessID.......................................................125 16 FMarker........................................................125 17 RFMarkInt......................................................126 18 SFMarkInt......................................................126 19 IFMarkInt......................................................127 20 InitialR2T.....................................................127 21 BidiInitialR2T.................................................127 22 ImmediateData..................................................128 23 DataPDULength..................................................129 24 FirstBurstSize.................................................129 25 LogoutLoginMinTime.............................................130 26 LogoutLoginMaxTime.............................................130 27 EnableACA......................................................130 28 MaxOutstandingR2T..............................................131 29 DataOrder......................................................131 30 BootSession....................................................131 31 The Glen-Turner Vendor Specific Key Format.....................131 Full Copyright Statement............................................133 Satran, J. Standards-Track, Expire November 2001 8 iSCSI April 19, 2001 1. Overview 1.1 SCSI Concepts The SCSI Architecture Model-2 [SAM2] describes in detail the architecture of the SCSI family of I/O protocols. This section provides a brief background to familiarize readers with the terminology of the SCSI architecture. At the highest level, SCSI is a family of interfaces for requesting services from I/O devices, including hard drives, tape drives, CD and DVD drives, printers, and scanners. In SCSI parlance, an individual I/O device is called a "logical unit" (LU). SCSI is a client-server architecture. Clients of a SCSI interface are called "initiators". Initiators issue SCSI "commands" to request service from a logical unit. The "device server" on the logical unit accepts SCSI commands and executes them. A "SCSI transport" maps the client-server SCSI protocol to a specific interconnect. Initiators are one endpoint of a SCSI transport. The "target" is the other endpoint. A target can have multiple Logical Units (LUs) behind it. Each Logical Unit has an address within a target called a Logical Unit Number (LUN). A SCSI task is a SCSI command or possibly a linked set of SCSI commands. Some LUs support multiple pending (queued) tasks but the queue of tasks is managed by the target. The target uses an initiator provided "task tag" to distinguish between tasks. Only one command in a task can be outstanding at any given time. Each SCSI command results in an optional data phase and a required response phase. In the data phase, information can travel from the initiator to target (e.g., WRITE), target to initiator (e.g., READ), or in both directions. In the response phase, the target returns the final status of the operation, including any errors. A response terminates a SCSI command. For performance reasons, iSCSI allows a "phase-collapse" (e.g., command and its associated data may be shipped together from initiator to target and data and responses may be shipped together from targets). Command Descriptor Blocks (CDB) is the data structure used to contain the command parameters that are to be handed by an initiator to a target. The CDB content and structure is defined by [SAM] and device- type specific SCSI standards. Satran, J. Standards-Track, Expire November 2001 9 iSCSI April 19, 2001 1.2 iSCSI Concepts and Functional Overview The iSCSI protocol is a mapping of the SCSI remote procedure invocation model over the TCP protocol. In keeping with similar protocols, the initiator and target divide their communications into messages. This document uses the term "iSCSI protocol data unit" (iSCSI PDU) for these messages. The iSCSI transfer direction is defined with regard to the initiator. Outbound or outgoing transfers are transfers from initiator to target, while inbound or incoming transfers are from target to initiator. An iSCSI task is an iSCSI request for which a response is expected. 1.2.1 Layers and Sessions To specify initiator and target actions and how they relate to transmitted and received Protocol Data Units the following conceptual layering model is used: -the SCSI layer builds/receives SCSI CDBs (Command Descriptor Blocks) and relays/receives them with the remaining command execute parameters (cf. SAM-2) to/from -> -the iSCSI layer that builds/receives iSCSI PDUs and relays/receives them to/from one or more TCP connections that form an initiator-target "session". Communication between the initiator and target occurs over one or more TCP connections. The TCP connections carry control messages, SCSI commands, parameters and data within iSCSI Protocol Data Units (iSCSI PDUs). The group of TCP connections that link an initiator with a target, form a session (loosely equivalent to a SCSI I-T nexus). A session is defined by a session ID that is composed of an initiator part and a target part. TCP connections can be added and removed from a session. Connections within a session are identified by a connection ID (CID). Across all connections within a session, an initiator sees one "target image". All target identifying elements, like LUN, are the same. In addition, across all connections within a session, a target sees one "initiator image". Initiator identifying elements like the Initiator Task Tag, can be used to identify the same entity regardless of the connection on which they are sent or received. Satran, J. Standards-Track, Expire November 2001 10 iSCSI April 19, 2001 iSCSI targets and initiators MUST support at least one TCP connection and MAY support several connections in a session. 1.2.2 Ordering and iSCSI Numbering iSCSI uses Command and Status numbering schemes and a Data sequencing scheme. Command numbering is session-wide and is used for ordered command delivery over multiple connections. It can also be used as a mechanism for command flow control over a session. Status numbering is per connection and is used to enable missing status detection and recovery in the presence of transient or permanent communication errors. Data sequencing is per command or part of a command (R2T triggered sequence) and is used to detect missing data and/or R2T PDUs due to header digest errors. Normally, fields in the iSCSI PDUs communicate the Sequence Numbers between the initiator and target. During periods when traffic on a connection is unidirectional, iSCSI NOP-Out/In PDUs may be utilized to synchronize the command and status ordering counters of the target and initiator. 1.2.2.1 Command Numbering and Acknowledging iSCSI supports ordered command delivery within a session. All commands (initiator-to-target) are numbered. Any SCSI activity is related to a task (SAM-2). The task is identified by the Initiator Task Tag for the life of the task. Commands in transit from the initiator SCSI layer to the SCSI target layer are numbered by iSCSI; the number is carried by the iSCSI PDU as CmdSN (Command-Sequence-Number). The numbering is session-wide. All outgoing iSCSI PDUs that have a task association, except Data- Out, carry this number. CmdSNs are allocated by the initiator iSCSI within a 32-bit unsigned counter (modulo 2**32). Comparisons and arithmetic on CmdSN SHOULD use Serial Number Arithmetic as defined in [RFC1982] where SERIAL_BITS = 32. Commands meant for immediate delivery are marked as such through an immediate delivery flag. They carry the same CmdSN as that which would have been given to a non-immediate command but the CmdSN is not advanced for immediate commands. Satran, J. Standards-Track, Expire November 2001 11 iSCSI April 19, 2001 Not covered in this document are the means by which the SCSI layer may request immediate delivery for a command or by which iSCSI will decide by itself to mark a PDU for immediate delivery. If immediate delivery is used with task management commands, these commands may reach the SCSI target task management before the tasks they are supposed to act upon. However, their CmdSN is a good reference for what commands the immediate command was supposed to act upon. CmdSNs are significant only during command delivery to the target. Once the device serving part of the target SCSI has received a command, CmdSN ceases to be significant. During command delivery to the target, the allocated numbers are unique session wide. Except for the commands marked for immediate delivery the iSCSI target layer MUST deliver the commands to the SCSI target layer in the order specified by CmdSN. Commands marked for immediate delivery may be handed over by the iSCSI target layer to the SCSI target layer as soon as detected. iSCSI may avoid delivering some command to the SCSI layer if so required by some prior SCSI or iSCSI action (e.g., clear task set Task Management request received before all the commands it was supposed to act on). The initiator and target are assumed to have three registers that define the numbering mechanism: - CmdSN - the current command Sequence Number advanced by 1 on each command shipped except for commands marked for immediate delivery. - ExpCmdSN - the next expected command by the target. The target acknowledges all commands up to but not including this number. The target iSCSI layer sets the ExpCmdSN to the largest non-immediate CmdSN that it is able to deliver to the target SCSI layer plus 1 (no holes in the CmdSN sequence). - MaxCmdSN - the maximum number to be shipped. MaxCmdSN - ExpCmdSN defines the queuing capacity of the receiving iSCSI layer. The target MUST NOT transmit a MaxCmdSN that is more than 2**31 - 1 above the last ExpCmdSN. For non-immediate commands, the CmdSN field can take any value from ExpCmdSN to MaxCmdSN. For immediate commands, the CmdSN field can take any value from ExpCmdSN to MaxCmdSN+1. The target MUST silently ignore any command outside this range or Satran, J. Standards-Track, Expire November 2001 12 iSCSI April 19, 2001 duplicates within the range that have not been flagged with the retry bit (the X bit in the opcode). iSCSI initiators and targets MUST support the command numbering scheme. 1.2.2.2 Response/Status Numbering and Acknowledging Responses in transit from the target to the initiator are numbered. The StatSN (Status Sequence Number) is used for this purpose. StatSN is a counter maintained per connection. ExpStatSN is used by the initiator to acknowledge status. Status numbering starts after Login. During login, there is always only one outstanding command per connection and status numbering is not strictly needed but may be used as a sanity check. The login response includes an initial value for status numbering. To enable command recovery the target MAY maintain enough state information to enable data and status recovery after a connection failure. A target can discard all the state information maintained for recovery after the status delivery is acknowledged through ExpStatSN. A large difference between StatSN and ExpStatSN may indicate a failed connection. Initiators MUST undertake recovery actions if the difference is greater than 2**31-1. Initiators and Targets MUST support the response-numbering scheme. 1.2.2.3 Data Sequencing Data and R2T PDUs transferred as part of some command execution MUST be sequenced. The DataSN field is used for data sequencing. For input (read) data PDUs DataSN starts with 0 for the first data PDU of an input command and advances by 1 for each subsequent data PDU. For output data, PDUs DataSN starts with 0 for the first data PDU of a sequence (the initial unsolicited sequence or any data PDU sequence issued to satisfy a R2T) and advances by 1 for each subsequent data PDU. R2Ts are also sequenced per command - i.e. the first R2T has a DataSN of 0 and advances by 1 for each subsequent R2T. Unlike command and status, the data PDUs and R2Ts are not acknowledged except as implied by status. The DataSN field is meant to enable the initiator to detect missing data PDUs and simplify this operation at the target. Satran, J. Standards-Track, Expire November 2001 13 iSCSI April 19, 2001 For any given write command a target must have issue less than 2**32- 1 R2Ts. Any input or output data sequence MUST contain less than 2**32-1 numbered PDUs. 1.2.3 iSCSI Login The purpose of the iSCSI login is to enable a TCP connection for iSCSI use, authenticate the parties, negotiate the session's parameters, open a security association protocol, and mark the connection as belonging to an iSCSI session. A session is used to identify to a target all the connections with a given initiator that belong to the same I_T nexus. If an initiator and target are connected through more than one session, both the initiator and target perceive the other as a different entity on each session (a different I_T nexus in SAM-2 parlance). The targets listen on a well-known TCP port for incoming connections. The initiator begins the login process by connecting to that well- known TCP port. As part of the login process, the initiator and target MAY wish to authenticate each other and set a security association protocol for the session. This can occur in many different ways and is subject to negotiation. Negotiation and security associations executed before the Login Command are outside the scope of this document although they may realize a related function (e.g., establish a IPsec tunnel). The Login Command starts the iSCSI Login Phase. Within the Login Phase, negotiation is carried on through parameters of the Login Command and Response, and optionally through intervening Text Commands and Responses. The Login Response indicates the progress and/or concludes the Login Phase. Once suitable authentication has occurred, the target MAY authorize the initiator to send SCSI commands. How the target chooses to authorize an initiator is beyond the scope of this document. The target indicates a successful authentication and authorization by sending a login response with "login accept". Otherwise, it sends a response with a "login reject", which indicates that a session is not established and the connection is terminated. Satran, J. Standards-Track, Expire November 2001 14 iSCSI April 19, 2001 It is expected that iSCSI parameters will be negotiated after the security association protocol is established, if there is a security association. The login PDU includes a session ID that is composed of an initiator part ISID and a target part TSID. For a new session, the TSID is null. As part of the response, the target generates a TSID. Session specific parameters can be specified only for the first login of a session (TSID null)(e.g., the maximum number of connections that can be used for this session). Connection specific parameters, if any, can be specified for any login. Thus, a session is operational once it has at least one connection. Any PDU except login and text, which is sent on a TCP connection before this connection gets into full feature phase, is a protocol error. When received at the initiator and target such a PDU MUST cause the connection to terminate. At the target, closing the connection SHOULD be preceded by a Reject PDU sent to the initiator. 1.2.4 Text Mode Negotiation During login and thereafter some session or connection parameters are negotiated through an exchange of textual information. In "list" negotiation, the offering party sends a list of values for a key in its order of preference. The responding party answers with the first value from the list it supports and is allowed to use for the specific initiator. The value "none" MUST always be used to indicate a missing function. However, none is a valid selection only if it is explicitly offered and MAY be selected by omission (i.e., =none MAY be omitted). If a target is not supporting, or not allowed to use with a specific initiator, any of the offered options, it may use the value "reject". The values "none" and "reject" are reserved and must be used only as described here. The general format of text negotiation is: Offer-> =,,..., Answer-> = Satran, J. Standards-Track, Expire November 2001 15 iSCSI April 19, 2001 In "numerical" negotiations, the offering and responding party state a numerical value. The result of the negotiation is key dependent; usually the lower or the higher of the two values is used. 1.2.5 iSCSI Full Feature Phase Once the initiator is authorized to do so, the iSCSI session is in iSCSI full feature phase. The initiator may send SCSI commands and data to the various LUs on the target by wrapping them in iSCSI PDUs that go over the established iSCSI session. For SCSI commands that require data and/or parameter transfer, the (optional) data and the status for a command MUST be sent over the same TCP connection that was used to deliver the SCSI command. We call this "connection allegiance". Thus, if an initiator issues a READ command, the target MUST send the requested data, if any, followed by the status to the initiator over the same TCP connection that was used to deliver the SCSI command. If an initiator issues a WRITE command, the initiator MUST send the data, if any, for that command and the target MUST return R2T, if any, and the status over the same TCP connection that was used to deliver the SCSI command. Retransmission requests (SNACK PDUs) as well as the data and status that they generate MUST also use the same connection. However, consecutive commands that are part of a SCSI linked command- chain task MAY use different connections. Connection allegiance is strictly per-command and not per-task. During the iSCSI Full Feature Phase, the initiator and target MAY interleave unrelated SCSI commands, their SCSI Data and responses, over the session. Outgoing SCSI data (initiator to target user data or command parameters) is sent as either solicited data or unsolicited data. Solicited data is sent in response to Ready To Transfer (R2T) PDUs. Unsolicited data can be sent as part of an iSCSI command PDU ("immediate data") or in separate iSCSI data PDUs. An initiator may send unsolicited data either as immediate (up to the negotiated maximum PDU size) or in a separate PDU sequence (up to the negotiated limit)). All subsequent data has to be solicited. The maximum size of an individual data PDU or the immediate-part of the first unsolicited burst as well as the first burst size MAY be negotiated at login. Targets operate in either solicited (R2T) data mode or unsolicited (non R2T) data mode. In unsolicited mode, an initial R2T is implied. A target MAY separately enable immediate data without enabling the more general (separate data PDUs) form of unsolicited data. Satran, J. Standards-Track, Expire November 2001 16 iSCSI April 19, 2001 An initiator SHOULD honor a R2T data request for a valid outstanding command (i.e., carrying a valid Initiator Task Tag) provided the command is supposed to deliver outgoing data and the R2T specifies data within the command bounds. It is considered an error for an initiator to send unsolicited data PDUs to a target operating in R2T mode (only solicited data is allowed). It is also an error for an initiator to send more data, whether immediate or as separate PDUs, than the SCSI limit for first burst. At login, an initiator MAY request, to send data blocks and a first burst of any size; in this case, the target MUST indicate the size of the first burst and of the immediate and data blocks that it is ready to accept. The agreed upon limits for the first burst as well as the maximum data PDU are recorded (and are retrievable from) the disconnect-reconnect mode page. A target SHOULD NOT silently discard data and request retransmission through R2T. Initiators SHOULD NOT do any score boarding for data. The residual count calculation is to be performed by the targets. Incoming data is always implicitly solicited. SCSI data packets are matched to their corresponding SCSI commands by using Tags that are specified in the protocol. Initiator tags for pending commands are unique initiator-wide for a session. Target tags are not strictly specified by the protocol. It is assumed that these tags are used by the target to tag (alone or in combination with the LUN) the solicited data. Target tags are generated by the target and "echoed" by the initiator. The above mechanisms are designed to accomplish efficient data delivery and a large degree of control over the data flow. iSCSI initiators and targets MUST also enforce some ordering rules to achieve deadlock-free operation. Unsolicited data MUST be sent on every connection in the same order in which commands were sent. A target receiving data out of order SHOULD terminate the session. Each iSCSI session to a target is treated as if it originated from a different and logically independent initiator. 1.2.6 iSCSI Connection Termination Connection termination is assumed an exceptional event. Graceful TCP connection shutdowns are done by sending TCP FINs. Graceful connection shutdowns MUST only occur when there are no outstanding tasks that have allegiance to the connection. A target SHOULD respond rapidly to a FIN from the initiator by closing it's Satran, J. Standards-Track, Expire November 2001 17 iSCSI April 19, 2001 half of the connection after waiting for all outstanding commands that have allegiance to the connection to conclude and send their status. Connection termination with outstanding commands may require recovery actions. Connection termination is also required as a prelude to recovery. By terminating a connection before starting recovery, the initiator and target can avoid having stale PDUs being received after recovery. In this case, the initiator sends a Logout request on any of the operational connections of a session indicating what connection should be terminated. Logout can also be issued by an initiator at the explicit request of a target (through an Asynchronous Event PDU) or it can be performed autonomously by the target after announcing it to the initiator (through an Asynchronous Event PDU). 1.2.7 Naming and Addressing This section provides a summary of detail provided in the iSCSI Naming & Discovery draft [NDT]. All iSCSI initiators and targets are named. Each target or initiator is known by an iSCSI Name. The iSCSI Name is independent of the location of the initiator and target; two formats are provided that allow the use of existing naming authorities when generating them. One of these formats allows the use of a registered domain name as a naming authority; it is important not to confuse this with an address. The iSCSI Name is a UTF-8 text string, and is defined in [NDT]. iSCSI Names are used to provide: - a target identifier for configurations that present multiple targets behind a single IP address and port. - a method to recognize multiple paths to the same device on different IP addresses and ports. - a symbolic address for source and destination targets for use in third party commands. - an identifier for initiators and targets to enable them to recognize each other regardless of IP address and port mapping on intermediary firewalls. Satran, J. Standards-Track, Expire November 2001 18 iSCSI April 19, 2001 The initiator MUST present both its iSCSI Initiator Name and the iSCSI Target Name to which it wishes to connect during the login phase. A target also provides a default name called "iSCSI". This is not a globally unique name. An initiator can log into this default target name, and use a command called "SendTargets" to retrieve a list of iSCSI targets that exist at that address. iSCSI Names do not require special handling within iSCSI; they are opaque. iSCSI targets also have addresses. An iSCSI address specifies a single path on which to find an iSCSI target. The iSCSI Name is incorporated as part of the address. An iSCSI address is specified as a URL, such as: [:]/ Where is one of: - IPv4 address, in dotted decimal notation. Assumed if the name contains exactly four numbers, separated by dots (.), where each number is in the range 0..255. - IPv6 address, in dotted decimal notation. Assumed if the name contains more than four, but at most 16 numbers, separated by dots (.), where each number is in the range 0..255. - Fully Qualified Domain Name (host name). Assumed if the is neither an IPv4 nor an IPv6 address. and is the iSCSI name of the target being addressed. The in the address is optional; it specified the TCP port on which the target is listening for connections. If is not specified, a default port, to be assigned by IANA, will be assumed. The iSCSI address, or URL, is not generally used within normal connections between iSCSI initiators and targets; it is primarily used during discovery. Details are specified in [NDT]. Examples of iSCSI Names: fqn.com.disk-vendor.diskarrays.sn.45678 fqn.com.gateways.yourtargets.24 fqn.com.os-vendor.plan9.cdrom.12345 fqn.com.service-provider.users.customer235.host90 Satran, J. Standards-Track, Expire November 2001 19 iSCSI April 19, 2001 eui.02004567A425678D Examples of IPv4 addresses/names: 10.0.0.1/fqn.com.disk-vendor.diskarrays.sn.45678 10.0.0.2/iscsi Examples of IPv6 addresses/names: 12.5.7.10.0.0.1/fqn.com.gateways.yourtargets.24 12.5.6.10.0.0.2/iscsi For management/support tools as well as naming services that use a text prefix to express the protocol intended (as in http:// or ftp://) the following form MAY be used: iSCSI://[:port][/iSCSI-name] Examples: iSCSI://diskfarm1.acme.com/iscsi iSCSI://computingcenter.acme.com/eui.02004567A425678D iSCSI://computingcenter.acme.com:4002/fqn.com.gateways.yourtarg ets.24 To assist in providing a more human-readable user interface for devices containing iSCSI targets and initiators, a target or initiator may also provide an alias. This alias is a simple UTF-8 string, is not globally unique, and is never interpreted or used to identify an initiator or device within the iSCSI protocol. Its use is described in [NDT]. When a target has to act as an initiator for a third party command, it MAY use the iSCSI Initiator Name it learned during login as required by the authentication mechanism to the third party. To address targets and logical units within a target, SCSI uses a fixed length (8 bytes) uniform addressing scheme; in this document, we call those addresses SCSI reference addresses (SRA). To provide the target with the protocol specific addresses iSCSI relies on the SCSI aliasing mechanism (work in progress in T10). The aliasing support enables an initiator to associate protocol specific addresses with SRAs; the later can be used in subsequent commands. For iSCSI, a protocol specific address is a TCP address and an iSCSI Name. Satran, J. Standards-Track, Expire November 2001 20 iSCSI April 19, 2001 An initiator may use one of a few techniques to configure and/or discover the iSCSI Target Names to which it has access, along with their addresses. These techniques are discussed fully in [NDT]. 1.2.8 Message Synchronization and Steering 1.2.8.1 Rationale iSCSI presents a mapping of the SCSI protocol onto TCP. This encapsulation is accomplished by sending iSCSI PDUs that are of varying length. Unfortunately, TCP does not have a built-in mechanism for signaling message boundaries at the TCP layer. iSCSI overcomes this obstacle by placing the message length in the iSCSI message header. This serves to delineate the end of the current message as well as the beginning of the next message. In situations where IP packets are delivered in order from the network, iSCSI message framing is not an issue; messages are processed one after the other. In the presence of IP packet reordering (e.g., frames being dropped), legacy TCP implementations store the "out of order" TCP segments in temporary buffers until the missing TCP segments arrive, upon which the data must be copied to the application buffers. In iSCSI it is desirable to steer the SCSI data within these out of order TCP segments into the pre-allocated SCSI buffers rather than store them in temporary buffers. This decreases the need for dedicated reassembly buffers as well as the latency and bandwidth related to extra copies. Unfortunately, when relying solely on the "message length in the iSCSI message" scheme to delineate iSCSI messages, a missing TCP segment that contains an iSCSI message header (with the message length) makes it impossible to find message boundaries in subsequent TCP segments. The missing TCP segment(s) must be received before any of the following segments can be steered to the correct SCSI buffers (due to the inability to determine the iSCSI message boundaries). Since these segments cannot be steered to the correct location, they must be saved in temporary buffers that must then be copied to the SCSI buffers. Different schemes can be used to recover synchronization. One of these schemes is detailed in an Appendix C. To make those schemes work iSCSI implementations have to make sure that the appropriate protocol layers are provided with enough information to implement a synchronization and/or data steering mechanism. 1.2.8.2 Synch and Steering Functional Model Satran, J. Standards-Track, Expire November 2001 21 iSCSI April 19, 2001 We assume that iSCSI is implemented according to the following layering scheme: Satran, J. Standards-Track, Expire November 2001 22 iSCSI April 19, 2001 +----------------------------------+ | SCSI | +----------------------------------+ | iSCSI | +----------------------------------+ | Synch and Steering | | +-----------------------------+ | | | TCP | | | +-----------------------------+ | +----------------------------------+ | Lower Functional Layers (LFL) | +----------------------------------+ | IP | +----------------------------------+ | Link | +----------------------------------+ In this model, LFL can be IPsec (a mechanism changing the IP stream and invisible to TCP). We assume that Synch and Steering operates just underneath iSCSI. Note that an implementation may choose to place Synch and Steering somewhere else in the stack if it can translate the information kept by iSCSI in terms valid for the chosen layer. According to our model of layering, iSCSI considers the information it delivers to the Synch and Steering layer (headers and payloads) as a contiguous stream of bytes mapped to the positive integers from 0 to infinity. For all practical purposes, iSCSI is not supposed to have to handle infinitely long streams. The stream addressing scheme will wrap around at 2**32-1. It is also assumed that iSCSI will deliver to the layers beneath any PDU through an indivisible (atomic) operation. If a specific implementation does PDU delivery to the Synch and Steering layer through multiple operations it MUST bracket an operation set used to deliver a single PDU in a manner understandable to the Synch and Steering Layer. The Synch and Steering Layer (which itself is OPTIONAL) MUST retain the PDU end address within the stream for every delivered iSCSI PDU. To enable the Synch and Steering operation to perform Steering, additional information including identifying tags and buffer offsets MUST also be retained for every sent PDU. The Synch and Steering Layer is required to add to every sent data item (IP packet, TCP packet or some other superstructure) enough information to enable the Satran, J. Standards-Track, Expire November 2001 23 iSCSI April 19, 2001 receiver to steer it to a memory location independent of any other piece. If the transmission stream is built dynamically, this information is used to insert Synch and Steering information in the transmission stream (at first transmission or at re-transmission) either through a globally accessible table or a call-back mechanism. If the transmission stream is built statically, the Synch and Steering information is inserted in the transmission stream. The retained information can be released whenever the transmitted data is acknowledged by the receiver (in case of dynamically built streams by deletion from the global table or by an additional callback). On the outgoing path, the Synch and Steering layer MUST map the outgoing stream addresses from iSCSI stream addresses to TCP stream sequence numbers. On the incoming path, the Synch and Steering layer extracts the Synch and Steering information from the TCP stream. Then it helps deliver (steer) the data stream to its final location and/or recover iSCSI PDU boundaries when some TCP packets are lost or received out of order. The data stream seen by the receiving iSCSI layer is identical to the data stream that left the sending iSCSI layer. The Synch and Steering information is kept until the PDUs it refers to are completely processed by the iSCSI layer. On the incoming path, the Synch and Steering layer does not change the way TCP notifies iSCSI about in-order data arrival. All data placements, in-order or out-of-order, performed by the Synch and Steering layer are hidden from iSCSI. Satran, J. Standards-Track, Expire November 2001 24 iSCSI April 19, 2001 1.2.8.3 Synch and Steering and Other Encapsulation Layers We recognize that in many environments the following is a more appropriate layering model: +----------------------------------+ | SCSI | +----------------------------------+ | iSCSI | +----------------------------------+ | Upper Functional Layers (UFL) | +----------------------------------+ | Synch and Steering | | +-----------------------------+ | | | TCP | | | +-----------------------------+ | +----------------------------------+ | Lower Functional Layers (LFL) | +----------------------------------+ | IP | +----------------------------------+ | Link | +----------------------------------+ In this model, UFL can be TLS or some other transport conversion mechanism (a mechanism changing the TCP stream but transparent to iSCSI). To be effective and act on reception of TCP packets out of order, Synch and Steering has to be underneath UFL and Synch and Steering data has to be left out of any UFL transformation (encryption, compression, padding etc.). However, Synch and Steering MUST take into account the additional data inserted in the stream by UFL. Synch and Steering MAY also restrict the type of transformations UFL may perform on the stream. This makes implementation of Synch and Steering in the presence of otherwise opaque UFLs less attractive. 1.2.8.4 Synch/Steering and iSCSI PDU Size When a large iSCSI message is sent, the TCP segment(s) that contain the iSCSI header may be lost. The remaining TCP segment(s) up to the next iSCSI message need to be buffered (in temporary buffers) since the iSCSI header that indicates what SCSI buffers the data is to be Satran, J. Standards-Track, Expire November 2001 25 iSCSI April 19, 2001 steered to was lost. To minimize the amount of buffering, it is recommended that the iSCSI PDU size be restricted to a small value (perhaps a few TCP segments in length). During login, each end of the iSCSI session specifies the maximum size of an iSCSI PDU it will accept. Satran, J. Standards-Track, Expire November 2001 26 iSCSI April 19, 2001 2. iSCSI PDU Formats All multi-byte integers that are specified in formats defined in this document are to be represented in network byte order (i.e., big endian). Any bits not defined MUST be set to zero. Any reserved fields and values MUST be 0 unless specified otherwise. 2.1 iSCSI PDU Length and Padding iSCSI PDUs are padded to an integer number of 4 byte words. The padding bytes should be 0. 2.2 PDU Template, Header and Opcodes All iSCSI PDUs have one or more header segments and, optionally, a data segment. After the entire header segment group there MAY be a header-digest. The data segment MAY also be followed by a data- digest. The first segment, and in many cases the only segment, (Basic Header Segment or BHS) is a fixed-length 48-byte header segment. It may be followed by Additional Header Segments (AHS). Thus, when we have only a BHS (no data or digests) the size of the iSCSI PDU is 48 bytes. The overall structure of a PDU is as follows: Satran, J. Standards-Track, Expire November 2001 27 iSCSI April 19, 2001 Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0 / BHS / +/ / +---------------+---------------+---------------+---------------+ 48/ AHS (optional) / +/ / +---------------+---------------+---------------+---------------+ ---- +---------------+---------------+---------------+---------------+ m/ Header-Digest (optional) / +/ / +---------------+---------------+---------------+---------------+ n/ Data Segment(optional) / +/ / +---------------+---------------+---------------+---------------+ m/ Data-Digest (optional) / +/ / +---------------+---------------+---------------+---------------+ All PDU segments and digests are padded to an integer number of 4 byte words. The padding bytes should be 0. 2.2.1 Header Digest and Data Digest Optional header and data digests protect the integrity and authenticity of header and data, respectively. The digests, if present, are located, respectively, after the header and PDU-specific data and include the padding bytes. The digest types are negotiated during the login phase. The separation of the header and data digests is useful in iSCSI routing applications, where only the header changes when a message is forwarded. In this case, only the header digest should be re- calculated. 2.2.2 Basic Header Segment (BHS) The Basic Header Segment is 48 bytes long. The Opcode, TotalAHSLength and DataSegmentLength fields appear in all iSCSI PDUs. In addition, the Initiator Task Tag, Logical Unit Number, Satran, J. Standards-Track, Expire November 2001 28 iSCSI April 19, 2001 and Flags fields, when used, always appear in the same location in the header. Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|X|I| Opcode |F| Opcode-specific fields | | |P| | +---------------+---------------+---------------+---------------+ 4|TotalAHSLength | DataSegmentLength | +---------------+---------------+---------------+---------------+ 8| LUN or Opcode-specific fields | + + 12| | +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag or Opcode-specific fields | +---------------+---------------+---------------+---------------+ 20/ Opcode-specific fields / +/ / +---------------+---------------+---------------+---------------+ 48 2.2.2.1 X The X bit is used as a Retry/Restart indicator for request PDUs (PDUs from initiator to target). This bit is always 1 for response PDUs (PDUs from target to initiator). 2.2.2.2 I The I bit is used as immediate delivery marker for request PDUs (PDUs from initiator to target). This bit is always 1 for response PDUs (PDUs from target to initiator). 2.2.2.3 Opcode The Opcode indicates what type of iSCSI PDU the header encapsulates. The Opcodes are divided into two categories: initiator opcodes and target opcodes. Initiator opcodes are in PDUs sent by the initiators (request PDUs), and target opcodes are in PDUs sent by the target (response PDUs). Valid initiator opcodes defined in this specification are: Satran, J. Standards-Track, Expire November 2001 29 iSCSI April 19, 2001 0x00 NOP-Out (from initiator to target) 0x01 SCSI Command (encapsulates a SCSI Command Descriptor Block) 0x02 SCSI Task Management Command 0x03 Login Command 0x04 Text Command 0x05 SCSI Data-out (for WRITE operations) 0x06 Logout Command 0x10 SNACK Request Valid target opcodes are: 0x00 NOP-In (from target to initiator) 0x01 SCSI Response (contains SCSI status and possibly sense information or other response information) 0x02 SCSI Task Management Response 0x03 Login Response 0x04 Text Response 0x05 SCSI Data-in (for READ operations) 0x06 Logout Response 0x10 Ready To Transfer (R2T - sent by target to initiator when it is ready to receive data from initiator) 0x11 Asynchronous Message (sent by target to initiator to indicate certain special conditions) 0x2f Reject Initiator and target opcodes 0x30-0x3f are vendor specific codes. 2.2.2.4 Opcode-specific Fields These fields have different meanings for different PDUs. Bit 7 of the second byte is used as a Poll/Final bit (P/F bit) for some iSCSI PDUs and MUST be 0 in all other iSCSI PDUs. When used as a Poll bit it indicates that an answer is required. When used as a Final bit it indicates a Final PDU in a logical sequence (e.g., the last Data PDU of unsolicited or solicited data PDU sequence or the perceived final Request/Response of the Login Phase). 2.2.2.5 TotalAHSLength Total length of all AHS header segments in 4 byte words including padding if any. 2.2.2.6 DataSegmentLength Satran, J. Standards-Track, Expire November 2001 30 iSCSI April 19, 2001 This is the data segment payload length in bytes (excluding padding). 2.2.2.7 LUN Some opcodes operate on a specific Logical Unit. The Logical Unit Number (LUN) field identifies which Logical Unit. If the opcode does not relate to a Logical Unit, this field either is ignored or may be used for some other purpose. The LUN field is 64-bits in accordance with [SAM2]. The exact format of this field can be found in the [SAM2] document. 2.2.2.8 Initiator Task Tag The initiator assigns a Task Tag to each iSCSI task that it issues. While a task exists this tag MUST uniquely identify it session-wide. 2.2.3 Additional Header Segment The general format of the additional header segments is: Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0| AHSType |AHSLength | AHS-Specific | +---------------+---------------+---------------+---------------+ 4/ AHS-Specific / +/ / +---------------+---------------+---------------+---------------+ x 2.2.3.1 AHSType The AHSType field is coded as follows: B7 - Drop Bit - if set to one this field can be ignored if not understood. B6 - Reserved - must be 0 B0-5 - AHS code 0 - Reserved 1 - Extended CDB 2 - Bi-Directional SCSI commands Expected Read Data Length 3-59 Reserved 60-63 Non iSCSI extensions 2.2.3.2 AHSLength Satran, J. Standards-Track, Expire November 2001 31 iSCSI April 19, 2001 This field contains the effective length in bytes of the AHS excluding AHSType and AHSLength (not including padding). The AHS is padded to a integer number of 4 byte words. 2.2.4 Extended CDB Additional Header Segment Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0| 0x01 |CDBLength-16 | Reserved (0) | +---------------+---------------+---------------+---------------+ 4/ ExtendedCDB...+padding / +/ / +---------------+---------------+---------------+---------------+ x 2.2.5 Bi-directional Expected Read-Data Length Additional Header Segment Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0| 0x02 |0x05 | Reserved (0) | +---------------+---------------+---------------+---------------+ 4| Expected Read-Data Length | +---------------+---------------+---------------+---------------+ 8 Satran, J. Standards-Track, Expire November 2001 32 iSCSI April 19, 2001 2.3 SCSI Command Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|X|I| 0x01 |F|R|W|0 0|ATTR | Reserved | CRN or Rsvd | +---------------+---------------+---------------+---------------+ 4|TotalAHSLength | DataSegmentLength | +---------------+---------------+---------------+---------------+ 8| Logical Unit Number (LUN) | + + 12| | +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag | +---------------+---------------+---------------+---------------+ 24| Expected Data Transfer Length | +---------------+---------------+---------------+---------------+ 28| CmdSN | +---------------+---------------+---------------+---------------+ 32| ExpStatSN or ExpDataSN | +---------------+---------------+---------------+---------------+ 36/ SCSI Command Descriptor Block (CDB) / +/ / +---------------+---------------+---------------+---------------+ 48| Digests if any... | +---------------+---------------+---------------+---------------+ / DataSegment - Command Data (optional) / +/ / +---------------+---------------+---------------+---------------+ 2.3.1 Flags and Task Attributes The flags for a SCSI Command are: b7 (F) set to 1 when the immediate data that accompany the command are all the data associated with this command. It is an error if the Length and Expected Length do not match and this bit is set to 1 b6 (R) set to 1 when input data is expected b5 (W) set to 1 when output data is expected b3-4 Reserved (MUST be 0) b0-2 used to indicate Task Attributes Satran, J. Standards-Track, Expire November 2001 33 iSCSI April 19, 2001 The Task Attributes (ATTR) can have one of the following integer values (see [SAM2] for details): 0 Untagged 1 Simple 2 Ordered 3 Head of Queue 4 ACA 2.3.2 CRN SCSI command reference number - if present in the SCSI execute command arguments (according to [SAM2]). 2.3.3 CmdSN - Command Sequence Number Enables ordered delivery across multiple connections in a single session. 2.3.4 ExpStatSN/ExpDataSN - Expected Status Sequence Number Command responses up to ExpStatSN-1 (mod 2**32) have been received (acknowledges status) on the connection. If the command is a retry (the X bit is 1) this field will contain the next consecutive input DataSN number expected by the initiator (no gaps) for this command in a previous execution. 2.3.5 Expected Data Transfer Length For unidirectional operations, the Expected Data Transfer Length field states the number of bytes of data involved in this SCSI operation. For a WRITE (W flag set to 1 and R flag set to 0) operation, the initiator uses this field to specify the number of bytes of data it expects to transfer for this operation. For a READ (W flag set to 0 and R flag set to 1) operation, the initiator uses this field to specify the number of bytes of data it expects the target to transfer to the initiator. It corresponds to the SAM-2 byte count. If the Expected Data Transfer Length for a WRITE and the length of immediate data part that follows the command (if any) are the same then no more data PDUs are expected to follow. In this case, the F bit MUST be set to 1. For bi-directional operations (both R and W flags are set to 1), this field states the number of data bytes involved in the outbound transfer. For bi-directional operations, an additional header segment Satran, J. Standards-Track, Expire November 2001 34 iSCSI April 19, 2001 MUST be present in the header sequence indicating the Expected Bi- directional Read Data Length. If this additional header segment is absent, the Expected Bi-directional Read Data Length is assumed 0. Upon completion of a data transfer, the target informs the initiator of how many bytes were actually processed (sent or received) by the target. This is done through residual counts. 2.3.6 CDB - SCSI Command Descriptor Block There are 16 bytes in the CDB field to accommodate the commonly used CDB. Whenever the CDB is larger than 16 bytes, an Extended CDB AHS MUST is used to contain the CDB spillover. 2.3.7 Command-Data Data Segment Some SCSI commands require additional parameter data to accompany the SCSI command. This data may be placed beyond the boundary of the iSCSI header (a data segment). Alternatively, user data (as from a WRITE operation) can be placed in the same PDU (both cases referred to as immediate data). Those data are governed by the general rules for solicited vs. unsolicited data. Satran, J. Standards-Track, Expire November 2001 35 iSCSI April 19, 2001 2.4 SCSI Response Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|1|1| 0x01 |1|Rsv|o|u|O|U|S| Reserved (0) |Status/Response| +---------------+---------------+---------------+---------------+ 4| Reserved (0) | DataSegmentLength | +---------------+---------------+---------------+---------------+ 8| Reserved (0) | + + 12| | +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag | +---------------+---------------+---------------+---------------+ 20| Basic Residual Count | +---------------+---------------+---------------+---------------+ 24| StatSN | +---------------+---------------+---------------+---------------+ 28| ExpCmdSN | +---------------+---------------+---------------+---------------+ 32| MaxCmdSN | +---------------+---------------+---------------+---------------+ 36| ExpDataSN or Reserved (0) | +---------------+---------------+---------------+---------------+ 40| R2TExpDataSN or Reserved (0) | +---------------+---------------+---------------+---------------+ 44| Bidi-Read Residual Count | +---------------+---------------+---------------+---------------+ 48| Digests if any... | +---------------+---------------+---------------+---------------+ / Sense Data (optional) or Response Data (optional) / +/ / +---------------+---------------+---------------+---------------+ 2.4.1 Byte 1 - Flags b0 (S) Status-Response selector - if 1, the response contains a valid SCSI status otherwise it contains a valid iSCSI Response b1 (U) set for Residual Underflow. In this case, the Basic Residual Count indicates how many bytes were not transferred out of those expected to be transferred. Satran, J. Standards-Track, Expire November 2001 36 iSCSI April 19, 2001 b2 (O) set for Residual Overflow. In this case, the Basic Residual Count indicates how many bytes could not be transferred because the initiator's Expected Data Transfer Length was too small. b3 (u) same as b0 but for the read-part of a bi-directional operation b4 (o) same as b1 but for the read-part of a bi-directional operation b5-6 Reserved Bits O and U are mutually exclusive and so are bits o and u. For a response (S=0) b0-b3 MUST be 0. 2.4.2 Status/Response The Status field is used to report the SCSI status of the command (as specified in [SAM2]). The Response is used to report a Service Response. The exact mapping of the iSCSI response codes to SAM service response symbols is outside the scope of this document. If a SCSI device error is detected while data from the initiator is still expected (the command PDU did not contain all the data and the target has not received a Data PDU with the final bit Set) the target MUST wait until it receives the a Data PDU with the F bit set before sending the Response PDU. Valid iSCSI Response codes are: 0x01 - Target Failure 0x02 - Delivery Subsystem Failure 0x03 - Unsolicited data rejected 0x04 - SNACK rejected 0x80-0xff - Reserved for Vendor-Unique Responses 2.4.3 Basic Residual Count The Basic Residual Count field is valid only in the case where either the U bit or the O bit is set. If neither bit is set, the Basic Residual Count field SHOULD be zero. If the U bit is set, the Basic Residual Count indicates how many bytes were not transferred out of those expected to be transferred. If the O bit is set, the Basic Residual Count indicates how many bytes could not be transferred because the initiator's Expected Data Transfer Length was too small. 2.4.4 Bidi-Read Residual Count Satran, J. Standards-Track, Expire November 2001 37 iSCSI April 19, 2001 The Bidi-Read Residual Count field is valid only in the case where either the u bit or the o bit is set. If neither bit is set, the Bidi-Read Residual Count field SHOULD be zero. If the u bit is set, the Bidi-Read Residual Count indicates how many bytes were not transferred to the initiator out of those expected to be transferred. If the o bit is set, the Bidi-Read Residual Count indicates how many bytes could not be transferred to the initiator because the initiator's Expected Bidi-Read Transfer Length was too small. 2.4.5 Sense or Response Data Segment iSCSI targets MUST support and enable autosense. If the Command Status was CHECK CONDITION (0x02), then the Data Segment contains sense data for the failed command. For some iSCSI responses, the response data segment MAY contain some response related information, (e.g., for a target failure it may contain a vendor specific detailed description of the failure). 2.4.6 ExpDataSN One past the largest DataSN in an input (read) data PDU the target has sent for the command. 0 means no data PDUs were sent. 2.4.7 R2TExpDataSN One past the largest DataSN in a R2T PDU the target has sent for the command. 0 means no R2T PDUs were sent. 2.4.8 StatSN - Status Sequence Number StatSN is a Sequence Number that the target iSCSI layer generates per connection and that in turn enables the initiator to acknowledge status reception. StatSN is incremented by 1 for every response/status sent on a connection except for responses sent as a result of a retry or SNACK. For responses sent because of retry the StatSN used MUST be the same as the first time the PDU was sent unless the connection was restarted since then. 2.4.9 ExpCmdSN - Next Expected CmdSN from this Initiator ExpCmdSN is a Sequence Number that the target iSCSI returns to the initiator to acknowledge command reception. It is used to update a local register with the same name. Satran, J. Standards-Track, Expire November 2001 38 iSCSI April 19, 2001 2.4.10 MaxCmdSN - Maximum CmdSN Acceptable from this Initiator MaxCmdSN is a Sequence Number that the target iSCSI returns to the initiator to indicate the maximum CmdSN the initiator can send. It is used to update a local register with the same name. MaxCmdSN and ExpCmdSN are processed as follows: -if the PDU MaxCmdSN is less than the PDU ExpCmdSN (in Serial Arithmetic Sense and with a difference bounded by 2**31-1), they are both ignored -if the PDU MaxCmdSN is less than the local MaxCmdSN (in Serial Arithmetic Sense and with a difference bounded by 2**31-1), it is ignored; else it updates the local MaxCmdSN -if the PDU ExpCmdSN is less than the local ExpCmdSN (in Serial Arithmetic Sense and with a difference bounded by 2**31-1), it is ignored; else it updates the local ExpCmdSN This sequence is required as updates may arrive out of order because they travel on different TCP connections. Satran, J. Standards-Track, Expire November 2001 39 iSCSI April 19, 2001 2.5 SCSI Task Management Command Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|X|I| x02 |0| Function | Reserved (0) | +---------------+---------------+---------------+---------------+ 4| Reserved (0) | +---------------+---------------+---------------+---------------+ 8| Logical Unit Number (LUN) or Reserved (0) | + + 12| | +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag | +---------------+---------------+---------------+---------------+ 20| Referenced Task Tag or Reserved (0x'ffffffff') | +---------------+---------------+---------------+---------------+ 24| CmdSN | +---------------+---------------+---------------+---------------+ 28| ExpStatSN | +---------------+---------------+---------------+---------------+ 32/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 48 2.5.1 Function The Task Management functions provide an initiator with a way to explicitly control the execution of one or more Tasks. The Task Management functions are summarized as follows (for a more detailed description see the [SAM2] document): 1 Abort Task - aborts the task identified by the Referenced Task Tag field. 2 Abort Task Set - aborts all Tasks issued by this initiator on the Logical Unit. 3 Clear ACA - clears the Auto Contingent Allegiance condition. 4 Clear Task Set - Aborts all Tasks (from all initiators) for the Logical Unit. 5 Logical Unit Reset 6 Target Warm Reset 7 Target Cold Reset Satran, J. Standards-Track, Expire November 2001 40 iSCSI April 19, 2001 For all these functions, if executed, the SCSI Task Management Response MUST be returned using the Initiator Task Tag to identify the operation for which it is responding. For the , the target MUST enter a Unit Attention Condition for all other attached initiators to inform them that all pending tasks are cancelled. After reporting the Unit Attention Condition, if enabled by the Logical Unit Control Mode Page bit EnableACA, the target enters the ACA state for any initiator for which it had pending tasks. For the and functions, the target cancels all pending operations and are both equivalent to the Target Reset as specified by SAM-2. The target MUST enter a Unit Attention Condition for all attached initiators notifying them that the target is being reset. In addition, for the , after reporting the Unit Attention Condition, if enabled by the Logical Unit Control Mode Page bit EnableACA, the target enters the ACA state on all sessions and all LUs on which the condition was reported. In addition, for the the target then MUST terminate all of its TCP connections to all initiators (all sessions are terminated). However, if the target finds that it cannot send the required response or AEN, it MUST continue the reset operation and it SHOULD log the condition for later retrieval. The logging operation MUST be reported through the target MIB. Further actions on reset functions are specified in the relevant SCSI documents for the specific class of devices. 2.5.2 Referenced Task Tag Initiator Task Tag of the task to be aborted - for abort task Satran, J. Standards-Track, Expire November 2001 41 iSCSI April 19, 2001 2.6 SCSI Task Management Response Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|1|1| 0x02 |0| Reserved (0) | +---------------+---------------+---------------+---------------+ 4| Reserved (0) | +---------------+---------------+---------------+---------------+ 8| Logical Unit Number (LUN) | + + 12| | +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag | +---------------+---------------+---------------+---------------+ 20| Referenced Task Tag or Reserved (0x'ffffffff') | +---------------+---------------+---------------+---------------+ 24| StatSN | +---------------+---------------+---------------+---------------+ 28| ExpCmdSN | +---------------+---------------+---------------+---------------+ 32| MaxCmdSN | +---------------+---------------+---------------+---------------+ 36| Response | Reserved (0) | +---------------+---------------+---------------+---------------+ 40/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 48 For the functions , the target performs the requested Task Management function and sends a SCSI Task Management Response back to the initiator. The target provides a Response, which may take on the following values: 0 Function Complete 1 Task was not in task set 2 LUN does not exist 255 Function Rejected For the and functions, the target cancels all pending operations. If SCSI control mode enables Satran, J. Standards-Track, Expire November 2001 42 iSCSI April 19, 2001 AE reporting, the target MUST send an Asynchronous Event to all attached initiators notifying them that the target has been reset. For the the target MUST then close all of its TCP connections to all initiators (terminates all sessions). The mapping of the response code into a SCSI service response code is outside the scope of this document. 2.6.1 Referenced Task Tag Initiator Task Tag of the task not found used in conjunction with Response value 1. It MUST be set to 0x'ffffffff' in other cases. Satran, J. Standards-Track, Expire November 2001 43 iSCSI April 19, 2001 2.7 SCSI Data-out & SCSI Data-in The typical data transfer specifies the length of the data payload, the Target Transfer Tag provided by the receiver for this data transfer, and a buffer offset. The typical SCSI Data PDU for WRITE (from initiator to target) has the following format: Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|0|0| 0x05 |F| Reserved (0) | +---------------+---------------+---------------+---------------+ 4| Reserved (0) | DataSegmentLength | +---------------+---------------+---------------+---------------+ 8| LUN or Reserved (0) | + + 12| | +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag | +---------------+---------------+---------------+---------------+ 20| Target Transfer Tag or (0x'ffffffff') | +---------------+---------------+---------------+---------------+ 24| Reserved (0) | +---------------+---------------+---------------+---------------+ 28| ExpStatSN | +---------------+---------------+---------------+---------------+ 32| Reserved (0) | +---------------+---------------+---------------+---------------+ 36| DataSN | +---------------+---------------+---------------+---------------+ 40| Buffer Offset | +---------------+---------------+---------------+---------------+ 44| Reserved (0) | +---------------+---------------+---------------+---------------+ 48| Digests if any... | +---------------+---------------+---------------+---------------+ / DataSegment / +/ / +---------------+---------------+---------------+---------------+ Satran, J. Standards-Track, Expire November 2001 44 iSCSI April 19, 2001 The typical SCSI Data packet for READ (from target to initiator) has the following format: Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|1|1| 0x05 |F| (0) |O|U|S| Reserved (0) |Status or Rsvd | +---------------+---------------+---------------+---------------+ 4| Reserved (0) | DataSegmentLength | +---------------+---------------+---------------+---------------+ 8| Reserved (0) | + + 12| | +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag | +---------------+---------------+---------------+---------------+ 20| Reserved (0) | +---------------+---------------+---------------+---------------+ 24| StatSN or Reserved (0) | +---------------+---------------+---------------+---------------+ 28| ExpCmdSN | +---------------+---------------+---------------+---------------+ 32| MaxCmdSN | +---------------+---------------+---------------+---------------+ 36| DataSN | +---------------+---------------+---------------+---------------+ 40| Buffer Offset | +---------------+---------------+---------------+---------------+ 44| Residual Count | +---------------+---------------+---------------+---------------+ 48| Digests if any... | +---------------+---------------+---------------+---------------+ / DataSegment / +/ / +---------------+---------------+---------------+---------------+ 2.7.1 F (Final) Bit For outgoing data, this bit is 1 for the last PDU of unsolicited data or the last PDU of a sequence answering a R2T. Satran, J. Standards-Track, Expire November 2001 45 iSCSI April 19, 2001 For incoming data, this bit is 1 for the last input data PDU associated with the command (even if it includes the status). 2.7.2 Target Transfer Tag On outgoing data, the Target Transfer Tag is provided to the target if the transfer is honoring a R2T. In this case, the Target Transfer Tag field is a replica of the Target Transfer Tag provided with the R2T. The Target Transfer Tag values are not specified by this protocol except that the all-bits-one value (0x'ffffffff') is reserved and means that the Target Transfer Tag is not supplied. If the Target Transfer Tag is provided then the LUN field MUST hold a valid value and be consistent with whatever was specified with the command, otherwise the LUN field is reserved. 2.7.3 StatSN This field MUST be set only if the S bit is set to 1 2.7.4 DataSN For input (read) data PDUs, the DataSN is the data PDU number (starting with 0) within the data transfer for the command identified by the Initiator Task Tag. For output (write) data PDUs, the DataSN is the data PDU number (starting with 0) within the current output sequence. The current output sequence is identified by the Initiator Task Tag (for unsolicited data) or is a data sequence generated for one R2T (for data solicited through R2T). Any input or output data sequence MUST contain less than 2**32-1 numbered PDUs. 2.7.5 Buffer Offset The Buffer Offset field contains the offset of this PDU payload data against the complete data transfer. The sum of the buffer offset and length should not exceed the expected transfer length for the command. Satran, J. Standards-Track, Expire November 2001 46 iSCSI April 19, 2001 Input data ordering is governed by a disconnect-reconnect mode page bit (EMDP). If this bit is 0 the target MUST deliver packets in increasing buffer offset order. Output data within a burst (initial or any data PDU sequence that fulfils a R2T) MUST be delivered in increasing buffer offset order. 2.7.6 DataSegmentLength This is the data payload length of a SCSI Data-In or SCSI Data-Out PDU; sending of 0 length data segments should be avoided. 2.7.7 Flags The last SCSI Data packet sent from a target to an initiator for a particular SCSI command that completed successfully may also optionally contain the Command Status for the data transfer. In this case, Sense Data cannot be sent together with the Command Status. If the command is completed with an error, then the response and sense data MUST be sent in a SCSI Response PDU (i.e., MUST NOT be sent in a SCSI Data packet). For Bi-directional commands the status MUST be sent in a SCSI Response PDU. b0 S (status)- set to indicate that the Command Status field contains status. If this bit is set to 1 the F bit MUST also be set to 1 b1-2 as in an SCSI Response b3-6 not used (should be set to 0) The fields StatSN, Command Status, Residual Count have meaningful content only if the S bit is set to 1. Satran, J. Standards-Track, Expire November 2001 47 iSCSI April 19, 2001 2.8 Text Command The Text Command is provided to allow the exchange of information and for future extensions. It permits the initiator to inform a target of its capabilities or to request some special operations. Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|X|I| 0x04 |F| Reserved (0) | +---------------+---------------+---------------+---------------+ 4| Reserved (0) | DataSegmentLength | +---------------+---------------+---------------+---------------+ 8| Reserved (0) | + + 12| | +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag | +---------------+---------------+---------------+---------------+ 20| Reserved (0) | +---------------+---------------+---------------+---------------+ 24| CmdSN | +---------------+---------------+---------------+---------------+ 28| ExpStatSN | +---------------+---------------+---------------+---------------+ 32/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 48| Digests if any... | +---------------+---------------+---------------+---------------+ / DataSegment (Text) / +/ / +---------------+---------------+---------------+---------------+ 2.8.1 F (Final) Bit When set to 1 it indicates that his is the last or only text command in a sequence of commands; otherwise it indicates that more commands will follow. 2.8.2 Initiator Task Tag The initiator assigned identifier for this Text Command. Satran, J. Standards-Track, Expire November 2001 48 iSCSI April 19, 2001 If the command is sent as part of a sequence of commands (e.g., the Login Phase or a sequence of Text commands) the Initiator Task Tag MUST be the same for all the commands within the sequence (similar to linked SCSI commands). 2.8.3 Text The initiator sends the target a set of key=value or key=list pairs encoded in UTF-8 Unicode. The key and value are separated by a '=' (0x3D) delimiter. Many key=value pairs can be included in the Text block by separating them with null (0x00) delimiters. A list is a set of values separated by comma (0x2C). Large binary items can be encoded using their hexadecimal representation (e.g., 8190 is 0x1FFE) or decimal representation. The maximum length of an individual value (not its string representation) is 255 bytes. The data length of a text command or response SHOULD be less than 4096 bytes. No key SHOULD contain more than 255 characters. Character strings are represented as plain text. Numeric and binary values are represented using either decimal numbers or the hexadecimal 0x'ffff' notation. The result is adjusted to the specific key. The target responds by sending its response back to the initiator. The response text format is similar to the request text format. Some basic key=value pairs are described in Appendix A and D. All of these keys, except for the X- extension format, MUST be supported by iSCSI initiators and targets. Manufacturers may introduce new keys by prefixing them with X- followed by their (reversed) domain name, for example the company owning the domain acme.com can issue: X-com.acme.bar.foo.do_something=0000000000000003 Any other key not understood by the target may be ignored without affecting basic function. If the Text Response does not contain a key that was requested, the initiator must assume that the key was not understood by the target or, whenever appropriate, that the response was "none". Text operations are usually meant for parameter setting/negotiations but can be used also to perform some active operations. Satran, J. Standards-Track, Expire November 2001 49 iSCSI April 19, 2001 It is recommended that Text operations that will take a long time should be placed in their own Text command. A session may have only one outstanding text command or text command sequence at any given time. 2.9 Text Response The Text Response PDU contains the target's responses to the initiator's Text Command. The format of the Text field matches that of the Text Command. Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|1|1| 0x04 |F| Reserved (0) | +---------------+---------------+---------------+---------------+ 4| Reserved (0) | DataSegmentLength | +---------------+---------------+---------------+---------------+ 8| Reserved (0) | + + 12| | +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag | +---------------+---------------+---------------+---------------+ 20| Reserved (0) | +---------------+---------------+---------------+---------------+ 24| StatSN | +---------------+---------------+---------------+---------------+ 28| ExpCmdSN | +---------------+---------------+---------------+---------------+ 32| MaxCmdSN | +---------------+---------------+---------------+---------------+ 36/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 48| Digests if any... | +---------------+---------------+---------------+---------------+ / DataSegment (Text) / +/ / +---------------+---------------+---------------+---------------+ 2.9.1 F (Final) Bit Satran, J. Standards-Track, Expire November 2001 50 iSCSI April 19, 2001 When set to 1 in response to a text command with the Final bit set to 1 the F bit indicates that the target has finished it's operation. Otherwise if set to 0 in response to a text command with the Final Bit set to 1 it indicates that the target has more work to do (invites a follow-on text command). A text response with the F bit set to 1 in response to a text command with the F bit set to 0 is a protocol error. 2.9.2 Initiator Task Tag The Initiator Task Tag matches the tag used in the initial Text Command or the Login Initiator Task Tag. 2.9.3 Text Response Data The Text Response Data Segment contains responses in the same key=value format as the Text Command and with the same length and coding constraints. Appendix C lists some basic Text Commands and their Responses. If the Text Response does not contain a key that was requested, the initiator must assume that the key was not understood by the target or that the answer is =none. Text response key=value pairs MUST be delivered in the same order as the command key=value pairs whenever applicable. Satran, J. Standards-Track, Expire November 2001 51 iSCSI April 19, 2001 2.10 Login Command After establishing a TCP connection between an initiator and a target, the initiator MUST issue a Login Command to gain further access to the target's resources. A Login Command MUST NOT be issued more than once on an iSCSI TCP connection. Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|0|0| 0x03 |F| Reserved (0)| Version-max | Version-min | +---------------+---------------+---------------+---------------+ 4| Reserved (0) | DataSegmentLength | +---------------+---------------+---------------+---------------+ 8| CID | Reserved (0) | +---------------+---------------+---------------+---------------+ 12| ISID |TSID | +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag | +---------------+---------------+---------------+---------------+ 20| Reserved (0) | +---------------+---------------+---------------+---------------+ 24| CmdSN or Reserved (0) | +---------------+---------------+---------------+---------------+ 28| ExpStatSN or Reserved (0) | +---------------+---------------+---------------+---------------+ 32/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 48/ DataSegment - Login Parameters in Text Command Format / +/ / +---------------+---------------+---------------+---------------+ 2.10.1 X - Restart If this bit is set to 1 then this command is an attempt to reinstate a failed connection. CID does not change and this command performs first the logout function of the old connection if an explicit logout was not performed earlier. In sessions with a single connection, this may imply the opening of a second connection with the sole purpose of cleaning-up the first. Targets should support opening a second Satran, J. Standards-Track, Expire November 2001 52 iSCSI April 19, 2001 connection even when not supporting multiple connections in full feature phase. 2.10.2 F (Final) Bit If set to 1 indicates that the initiator has no more parameters to set. 2.10.3 Version-max Maximum Version number supported. 2.10.4 Version-min Minimum Version supported The version number of the current draft is 0x1. 2.10.5 CID This is a unique ID for this connection within the session. 2.10.6 ISID This is an initiator-defined session-identifier. It MUST be the same for all connections within a session. 2.10.7 CmdSN Is significant only if TSID is zero and indicates the starting Command Sequence Number for this session; it MUST be zero for all other instances. 2.10.8 ExpStatSN This is ExpStatSN for the old connection. This field is valid only if the X bit is set to 1. 2.10.9 Login Parameters The initiator MAY provide some basic parameters in order to enable the target to determine if the initiator may use the target's Satran, J. Standards-Track, Expire November 2001 53 iSCSI April 19, 2001 resources and the initial text parameters for the security exchange. The format of the parameters is as specified for the Text Command. Keys and their explanations are listed in the Appendixes. Satran, J. Standards-Track, Expire November 2001 54 iSCSI April 19, 2001 2.11 Login Response The Login Response indicates the progress and/or end of the login phase. Note that after security is established, the login response is authenticated. Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|1|1| 0x03 |F| Reserved (0)| Version-max | Version-active| +---------------+---------------+---------------+---------------+ 4| Reserved (0) | DataSegmentLength | +---------------+---------------+---------------+---------------+ 8| Reserved (0) | +---------------+---------------+---------------+---------------+ 12| ISID |TSID | +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag | +---------------+---------------+---------------+---------------+ 20| Reserved (0) | +---------------+---------------+---------------+---------------+ 24| InitStatSN | +---------------+---------------+---------------+---------------+ 28| ExpCmdSN | +---------------+---------------+---------------+---------------+ 32| MaxCmdSN | +---------------+---------------+---------------+---------------+ 36| Status-Class | Status-Detail | Reserved (0) | +---------------+---------------+---------------+---------------+ 40/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 48| Digests if any... | +---------------+---------------+---------------+---------------+ / DataSegment - Login Parameters in Text Command Format / +/ / +---------------+---------------+---------------+---------------+ 2.11.1 Version-max This is the highest version number supported by the target. 2.11.2 Version-active/lowest Satran, J. Standards-Track, Expire November 2001 55 iSCSI April 19, 2001 Indicates the version supported (the highest version supported by the target and initiator). If the target is not supporting a version within the range specified by the initiator, the target rejects the login and this field indicates the lowest version supported by the target. 2.11.3 InitStatSN This is the starting status Sequence Number for this connection. The value is relevant for all subsequent responses. If the login phase involves two login responses (a partial response and a final response) then the InitStatSN in each of them will hold for the subsequent responses. This field is valid only if the Status Class is 0. 2.11.4 Status-Class and Status-Detail The Status returned in a Login Response indicates the status of the login request. The status includes: Status-Class Status-Detail The Status-Class is sufficient for a simple initiator to use when handling errors, without having to look at the Status-Detail. The Status-Detail allows finer-grained error recovery for more sophisticated initiators, as well as better information for error logging. The status classes are as follows: 0 - Success - indicates that the iSCSI target successfully received, understood, and accepted the request. The numbering fields (InitStatSN, ExpCmdSN, MaxCmdSN are valid only if Status-Class is 0). 1 - Redirection - indicates that further action must be taken by the initiator to complete the request. This is usually due to the target moving to a different address. All of the status class 1 responses MUST return one or more text key parameters of the type "TargetAddress", which indicates the target's new address. 2 - Initiator Error - indicates that the initiator likely caused the error. This MAY be due to a request for a resource for which the initiator does not have permission. Satran, J. Standards-Track, Expire November 2001 56 iSCSI April 19, 2001 3 - Target Error - indicates that the target is incapable of fulfilling the request. The table below shows all of the currently allocated status codes. The codes are in hexadecimal; the first byte is the status class and the second byte is the status detail. The allowable state of the Final (F) bit in responses with each of the codes is also displayed. ----------------------------------------------------------------- Status | Code | F | Description |(hex) | bit | ----------------------------------------------------------------- Accept Login | 0000 | 1/0 | Login is OK, moving to Full Feature | | | Phase (F=1) or Operational Parameter | | | Negotiation (F=0). ----------------------------------------------------------------- Authenticate | 0001 | 0 | The iSCSI Target Name (ITN) exists and | | | authentication proceeds. ----------------------------------------------------------------- iSCSI Target | 0002 | 0 | The ITN must be provided Name required | | | for authentication to proceed. ----------------------------------------------------------------- Target Moved | 0101 | 1 | The requested ITN has moved Temporarily | | | temporarily to the address provided. ----------------------------------------------------------------- Target Moved | 0102 | 1 | The requested ITN has moved Permanently | | | permanently to the address provided. ----------------------------------------------------------------- Proxy Required| 0103 | 1 | The initiator must use an iSCSI | | | proxy for this target. | | | The address is provided. ----------------------------------------------------------------- Authentication| 0201 | 1 | The initiator authentication failed. Failed | | | ----------------------------------------------------------------- Forbidden | 0202 | 1 | The initiator is not allowed access Target | | | to the given target. ----------------------------------------------------------------- Not Found | 0203 | 1 | The requested ITN does not | | | exist at this address. ----------------------------------------------------------------- Target Removed| 0204 | 1 | The requested ITN has been | | | removed. No forwarding address is | | | provided. ----------------------------------------------------------------- Satran, J. Standards-Track, Expire November 2001 57 iSCSI April 19, 2001 Target | 0205 | 1 | Target is currently in use by Conflict | | | another initiator and does | | | not support multiple initiators. ----------------------------------------------------------------- Initiator | 0206 | 1 | Invalid TSID - no more connections SID error | | | accepted | | | ----------------------------------------------------------------- Missing | 0207 | 1 | Missing parameters (e.g., iSCSI parameter | | | Initiator and/or Target Name) ----------------------------------------------------------------- Target Error | 0300 | 1 | An error occurred in the iSCSI | | | target (out of resources, etc.). ----------------------------------------------------------------- Service | 0301 | 1 | The iSCSI service or target is not Unavailable | | | currently operational. This is | | | usually due to maintenance. ----------------------------------------------------------------- Unsupported | 0302 | 1 | The required version is not version | | | supported by the target. ----------------------------------------------------------------- If the Status is "accept login" (0x0000) and the F bit is 1, the initiator may proceed to issue SCSI commands. If the Status is "accept login" (0x0000) and the F bit is 0, the initiator may proceed to negote operational parameters. The target MUST not set the Status to 0x'0000' and the F bit to 1 if the Login Command had the F bit set to 0. If the Status Class is not 0, the initiator and target MUST close the TCP connection. If the target wishes to reject the login request for more than one reason, it should return the primary reason for the rejection. 2.11.5 TSID The TSID is an initiator identifying tag set by the target. It is valid only if the connection is accepted. 2.11.6 F (Final) bit Final bit is set to one in the Final Login Response. A Final bit of 0 indicates a "partial" response, which means "more negotiation needed". Satran, J. Standards-Track, Expire November 2001 58 iSCSI April 19, 2001 TSID MUST be returned in the partial response and the same value MUST be presented with the final response. Satran, J. Standards-Track, Expire November 2001 59 iSCSI April 19, 2001 2.12 NOP-Out Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|X|I| 0x00 |P| Reserved (0) | +---------------+---------------+---------------+---------------+ 4| Reserved (0) | DataSegmentLength | +---------------+---------------+---------------+---------------+ 8| LUN | + + 12| | +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag or Reserved (0x'ffffffff') | +---------------+---------------+---------------+---------------+ 20| Target Transfer Tag or Reserved (0x'ffffffff') | +---------------+---------------+---------------+---------------+ 24| CmdSN | +---------------+---------------+---------------+---------------+ 28| ExpStatSN | +---------------+---------------+---------------+---------------+ 32/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 48| Digests if any... | +---------------+---------------+---------------+---------------+ / DataSegment - Ping Data (optional) / +/ / +---------------+---------------+---------------+---------------+ The NOP-Out with the P bit set acts as a "ping command". This form of the NOP-Out can be used to verify that a connection is still active and all its components are operational. This command MAY use in-order delivery or immediate delivery. The NOP-Out may be useful in the case where an initiator has been waiting a long time for the response to some command, and the initiator suspects that there is some problem with the connection. When a target receives the NOP-Out with the Ping bit set, it should respond with a Ping Response, duplicating the data that was provided in the NOP-Out as much as possible. If the initiator does not receive the NOP-In within some time (determined by the initiator), or if the data returned by the NOP-In is different from the data that was in the NOP-Out, the initiator may conclude that there is a problem with the Satran, J. Standards-Track, Expire November 2001 60 iSCSI April 19, 2001 connection. The initiator then closes the connection and may try to establish a new connection. A NOP-Out should also be used to confirm a changed ExpStatSN if there is no other PDU to carry it for a long time. The NOP-Out can be sent by an initiator because of a NOP-In with the poll bit set. In this case the Target Tag copies the NOP-In value, the P bit MUST be 0 and I bit must be 1. 2.12.1 P (Ping) Bit Request a NOP-In 2.12.2 Initiator Task Tag An initiator assigned identifier for the operation. The NOP-Out MUST have the Initiator Task Tag set only if the P bit is 1. 2.12.3 Target Transfer Tag A target assigned identifier for the operation. The NOP-Out MUST have the Target Tag set only if it is issued in response to a NOP-In with the P bit one, in which case it copies the Target Transfer Tag from the NOP-In PDU. When the Target Transfer Tag is set, the LUN field MUST have the correct value for the task. 2.12.4 Ping Data Ping data is reflected in the Ping Response. Note that the length of the reflected data is limited to 4096 bytes and the initiator should avoid sending more than 4096 bytes. Satran, J. Standards-Track, Expire November 2001 61 iSCSI April 19, 2001 2.13 NOP-In Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|1|1| 0x00 |P| Reserved (0) | +---------------+---------------+---------------+---------------+ 4| Reserved (0) | DataSegmentLength | +---------------+---------------+---------------+---------------+ 8| LUN or Reserved (0) | + + 12| | +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag or Reserved (0x'ffffffff') | +---------------+---------------+---------------+---------------+ 20| Target Transfer Tag or Reserved (0x'ffffffff') | +---------------+---------------+---------------+---------------+ 24| StatSN | +---------------+---------------+---------------+---------------+ 28| ExpCmdSN | +---------------+---------------+---------------+---------------+ 32| MaxCmdSN | +---------------+---------------+---------------+---------------+ 36/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 48| Digests if any... | +---------------+---------------+---------------+---------------+ / DataSegment - Return Ping Data / +/ / +---------------+---------------+---------------+---------------+ When a target receives the NOP-Out with the P bit set, it MUST respond with a NOP-In with the same Initiator Task Tag that was provided in the NOP-Out Command. It SHOULD also duplicate up to first 4096 bytes of the initiator provided Ping Data. For such a response, the P bit MUST be 0. 2.13.1 P bit A target may issue a NOP-In on its own to test the connection and the state of the initiator. If the target wants to test the initiator, it sets the P bit to 1 in order to ask for an answer from the initiator. Satran, J. Standards-Track, Expire November 2001 62 iSCSI April 19, 2001 In this case the Initiator Task Tag MUST be 0x'ffffffff' and the Target Tag MUST be set to a valid value (not 0x'ffffffff'). The LUN field MUST also contain a valid LUN. If the target wants only to test the connection, the P bit is set to 0 and both tags MUST hold the reserved value 0x'ffffffff'. A target may also issue a NOP-In on its own to carry a changed CmdSN and/or MaxCmdSN if there is no other PDU to carry them for a long time. Whenever the NOP-In is not issued in response to a NOP-Out the StatSN field will contain as usual the next StatSN but StatSN for this connection is not advanced. 2.13.2 Target Transfer Tag A target assigned identifier for the operation. 2.13.3 LUN A LUN MUST be set to a correct value when the P bit is set to 1 and the Target Transfer Tag is set. Satran, J. Standards-Track, Expire November 2001 63 iSCSI April 19, 2001 2.14 Logout Command The Logout command is used to perform a controlled closing of a connection. An initiator MAY use a logout command to remove a connection from a session or to close an entire session. If an initiator intends to start recovery for a failing connection it MUST use either the Logout command to "clean-up" the target end of a failing connection and enable recovery to start, or use the restart option of the Login command for the same effect. In sessions with a single connection, this may imply the opening of a second connection with the sole purpose of cleaning-up the first. In this case, the restart option of the Login should be used. Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|0|I| 0x06 |1| Reserved (0) | +---------------+---------------+---------------+---------------+ 4| Reserved (0) | +---------------+---------------+---------------+---------------+ 8| CID or Reserved | Reserved (0) |Reason Code | +---------------+---------------+---------------+---------------+ 12| Reserved (0) | +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag | +---------------+---------------+---------------+---------------+ 20/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 28| ExpStatSN or (0) | +---------------+---------------+---------------+---------------+ 32/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 48 2.14.1 CID This is the connection ID of the connection to be closed (including closing the TCP stream). This field is valid only if the reason code is not "close session". Satran, J. Standards-Track, Expire November 2001 64 iSCSI April 19, 2001 2.14.2 ExpStatSN This is the last ExpStatSN value for the connection to be closed. 2.14.3 Reason Code Indicate the reason for Logout: 0 - closes the session 1 - closes the connections 2 - removes the connection for recovery 3 - removes the connection at target's request (requested through an Asynchronous Message) Satran, J. Standards-Track, Expire November 2001 65 iSCSI April 19, 2001 2.15 Logout Response The logout response is used by the target to indicate that the cleanup operation for the connection has completed. After Logout, the TCP connection referred by the CID MUST be closed at both ends (or all connections must be closed if the logout reason was session close). Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|1|1| 0x06 |1| Reserved (0) | +---------------+---------------+---------------+---------------+ 4/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag | +---------------+---------------+---------------+---------------+ 20/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 28| ExpCmdSN | +---------------+---------------+---------------+---------------+ 32| MaxCmdSN | +---------------+---------------+---------------+---------------+ 36| Response | Reserved (0) | +---------------------------------------------------------------+ 40/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 48 2.15.1 Response Logout response: 0 - connection closed successfully 1 - cleanup failed Satran, J. Standards-Track, Expire November 2001 66 iSCSI April 19, 2001 2.16 SNACK Request Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|0|1| 0x10 |1|Reserved(0)|S| | AddRuns | +---------------+---------------+---------------+---------------+ 4/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag or Reserved (0x'ffffffff') | +---------------+---------------+---------------+---------------+ 20| BegRun | +---------------+---------------+---------------+---------------+ 24| RunLength | +---------------+---------------+---------------+---------------+ 28| ExpStatSN/ExpDataSN | +---------------+---------------+---------------+---------------+ 32/ Additional Runs or Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 48 SNACK request is used to request retransmission of status or data PDUs from the target. The SNACK request indicates to the target the missed status or data runs, where a run is composed of an initial missed StatSN or DataSN and the number of additional missed Status or Data PDUs (0 means only the initial). If a SNACK includes more than one run those have to be in increasing order and non-overlapping; the SNACK implicitly acknowledges data or status PDUs indicated by the intervals between runs. 2.16.1 S If 1, indicates that this is a Status SNACK; otherwise it is a Data SNACK. The data SNACK for a command MUST precede implicit or explicit status acknowledgement for the given command. For a Data SNACK, the Initiator Task Tag MUST be set to the Initiator Task Tag of the referenced Command. Otherwise, it is reserved. iSCSI targets MUST support Status SNACK and MAY support Data SNACK. 2.16.2 AddRuns Satran, J. Standards-Track, Expire November 2001 67 iSCSI April 19, 2001 Runs are gaps in sequence numbers as perceived by the receiver. Each run is characterized by a starting sequence and a length. This field specifies the number of additional runs (0, 1, or 2 are the only valid values). 2.16.3 BegRun First missed DataSN or StatSN 2.16.4 RunLength Number of additional sequential missed DataSN or StatSN. If BegRun is the only one missing, RunLength MUST be 0. 2.16.5 ExpStatSN/ExpDataSN ExpStatSN if S is 1 otherwise ExpDataSN. 2.16.6 Additional Runs Contains 0, 1 or 2 additional double words - the first being the BegRun and the second the RunLength of the additional run. Satran, J. Standards-Track, Expire November 2001 68 iSCSI April 19, 2001 2.17 Ready To Transfer (R2T) Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|1|1| 0x10 |1| Reserved (0) | +---------------+---------------+---------------+---------------+ 4/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 16| Initiator Task Tag | +---------------+---------------+---------------+---------------+ 20| Target Transfer Tag | +---------------+---------------+---------------+---------------+ 24| StatSN | +---------------+---------------+---------------+---------------+ 28| ExpCmdSN | +---------------+---------------+---------------+---------------+ 32| MaxCmdSN | +---------------+---------------+---------------+---------------+ 36| DataSN | +---------------+---------------+---------------+---------------+ 40| Buffer Offset | +---------------+---------------+---------------+---------------+ 44| Desired Data Transfer Length | +---------------------------------------------------------------+ 48 When an initiator has submitted a SCSI Command with data passing from the initiator to the target (WRITE), the target may specify which blocks of data it is ready to receive. In general, the target may request that the data blocks be delivered in whichever order is convenient for the target at that particular instant. This information is passed from the target to the initiator in the Ready To Transfer (R2T) PDU. In order to allow write operations without an explicit initial R2T, the initiator and target MUST have agreed to do so by sending the InitialR2T=no key-pair to each other, which happens either during Login or through the Text Command/Response mechanism. A R2T MAY be answered with one or more SCSI Data-out PDUs with a matching Target Transfer Tag. If a R2T is answered with a single Data Satran, J. Standards-Track, Expire November 2001 69 iSCSI April 19, 2001 PDU, the Buffer Offset in the Data PDU MUST be the same as the one specified by the R2T. The data length of the Data PDU MUST not exceed the Desired Data Length specified in R2T. If the R2T is answered with a sequence of Data PDUs the Buffer Offset and Length must be within the range of those specified by R2T, the last PDU should have the F bit set to 1, the Buffer Offsets and Lengths for consecutive PDUs should form a continuous non-overlapping range and the PDUs should be sent in increasing offset order. The target may send several R2T PDUs (up to a negotiated number) and thus have a number of data transfers pending. Within a connection, outstanding R2Ts MUST be fulfilled by the initiator in the order in which they where received. 2.17.1 DataSN DataSN is the R2T PDU number (starting with 0) within the command identified by the Initiator Task Tag. The number of R2Ts in a command MUST be less than 0x'ffffffff'. 2.17.2 StatSN The StatSN field will contain as usual the next StatSN but StatSN for this connection is not advanced. 2.17.3 Desired Data Transfer Length and Buffer Offset The target specifies how many bytes it wants the initiator to send because of this R2T PDU. The target may request the data from the initiator in several chunks, not necessarily in the original order of the data. The target, therefore, also specifies a Buffer Offset that indicates the point at which the data transfer should begin, relative to the beginning of the total data transfer. The Desired Data Transfer Length should not be 0. 2.17.4 Target Transfer Tag The target assigns its own tag to each R2T request that it sends to the initiator. This tag can be used by the target to easily identify the data it receives. The Target Transfer Tag is copied in the outgoing data PDUs and is used by the target only. There is no protocol rule about Target Transfer Tag, but it is assumed that it is used to tag the response data to the target (alone or in combination with the LUN). Satran, J. Standards-Track, Expire November 2001 70 iSCSI April 19, 2001 2.18 Asynchronous Message An Asynchronous Message may be sent from the target to the initiator without corresponding to a particular command. The target specifies the status and reason for the event and sense data. Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|1|1| 0x11 |1| Reserved (0) | +---------------+---------------+---------------+---------------+ 4| Reserved (0) | DataSegmentLength | +---------------+---------------+---------------+---------------+ 8| Logical Unit Number (LUN) | + + 12| | +---------------+---------------+---------------+---------------+ 16/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 24| StatSN | +---------------+---------------+---------------+---------------+ 28| ExpCmdSN | +---------------+---------------+---------------+---------------+ 32| MaxCmdSN | +---------------+---------------+---------------+---------------+ 36|SCSI Event |iSCSI Event | Parameter1 or Reserved (0) | +---------------+---------------+---------------+---------------+ 40| Parameter2 or Reserved (0) | Parameter3 or Reserved (0) | +---------------+---------------+---------------+---------------+ 44| Reserved (0) | +---------------+---------------+---------------+---------------+ 48| Digests if any... | +---------------+---------------+---------------+---------------+ / DataSegment - Sense Data / +/ / +---------------+---------------+---------------+---------------+ Some Asynchronous Messages are strictly related to iSCSI while others are related to SCSI [SAM2]. An Asynchronous Message may contain both types of events. Satran, J. Standards-Track, Expire November 2001 71 iSCSI April 19, 2001 Please note that StatSN counts this PDU as an acknowledgeable event, allowing initiator and target state synchronization. 2.18.1 iSCSI Event The codes used for iSCSI Asynchronous Messages (Events) are: 0 No iSCSI Event 1 Target is being reset. 2 Target requests Logout - the Parameter1 field indicates on what CID. 3 Target indicates it will/has dropped the connection - the Parameter1 field will indicate on what CID while the Parameter2 field indicates, in seconds, the minimum time to reconnect and Parameter3 the maximum time to reconnect. 4 Target indicates it will/has dropped all connections - the Parameter2 field indicates, in seconds, the minimum time to reconnect and Parameter3 the maximum time to reconnect. Initiators can attempt to set/modify the values a target will use for Parameter2 and Parameter3 2.18.2 SCSI Event The following values are defined. (See [SAM2] for details): 0 No SCSI Asynchronous Event is reported. 1 A SCSI Asynchronous Event is reported in the sense data. Sense Data that accompanies the report, in the data segment, identifies the condition. Satran, J. Standards-Track, Expire November 2001 72 iSCSI April 19, 2001 2.19 Third Party Commands SCSI allows every addressable entity to be either an initiator or a target. In host-to-host communication, each such entity can take on the initiator role. In typical I/O operations between a host and a peripheral subsystem, the host plays the initiator role and the peripheral subsystem plays the target role. For EXTENDED COPY and other third party SCSI commands, that involve device-to-device communication, such as (EXTENDED) COPY and COMPARE, SCSI defines a copy-manager. The copy-manager takes on the role of initiator in the device-to-device communication. The copy-manager is the "original-target" of the command and acts as initiator for a (variable) number of the devices, which are called sources and destinations. Sources and destinations act as targets. The whole operation is described by one "master CDB" that is delivered to the copy-manager and a series of descriptor blocks; each descriptor block addresses a source and destination target, LU and a description of the work to be done in terms of blocks or bytes as required by the device types. The relevant SCSI standards do not require full support of the (EXTENDED) COPY or COMPARE, nor do they provide a detailed execution model. Enabling a FC copy-manager to support iSCSI sources and destinations is subject to coordination with T10. Satran, J. Standards-Track, Expire November 2001 73 iSCSI April 19, 2001 2.20 Reject Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|1|1| 0x2f |1| Reserved (0) | +---------------+---------------+---------------+---------------+ 4| Reserved (0) | DataSegmentLength | +---------------+---------------+---------------+---------------+ 8/ Reserved (0) / +/ / +---------------+---------------+---------------+---------------+ 40| Reason | Reserved (0) | First Bad Byte or Rsvd(0) | +---------------+---------------+---------------+---------------+ 44| Reserved (0) | +---------------+---------------+---------------+---------------+ 48| Digests if any... | +---------------+---------------+---------------+---------------+ xx/ Complete Header of Bad PDU / +/ / +---------------+---------------+---------------+---------------+ yy It may happen that a target receives a PDU with a format error (e.g., inconsistent fields etc.) or a digest error (e.g., invalid payload or header). The target returns the header (not including digest) of the PDU in error as the data of the response. 2.20.1 Reason The reject Reason is coded as follows: 1 - Format Error 2 - Header Digest Error 3 - Data (payload) Digest Error 4 - Data-SNACK Reject 5 - Command Retry Reject 15 - Full Feature Phase Command before login Some of the reject reasons terminate or prevent the creation of a task at the target and no retry is possible in those cases. Format error for a command, Command Retry Reject and Full Feature Phase Command before login are in this category. Satran, J. Standards-Track, Expire November 2001 74 iSCSI April 19, 2001 2.20.2 First Bad Byte For a format error reject, this is the offset of the first offending byte in the header. Satran, J. Standards-Track, Expire November 2001 75 iSCSI April 19, 2001 3. SCSI Mode Parameters for iSCSI This chapter describes fields and mode pages that control and report the behavior of the iSCSI protocol. All fields not described here MUST control the behavior of iSCSI devices as defined by the corresponding command set standard. The mode parameters can be set and retrieved by SCSI mode-set and mode-sense commands or with the iSCSI text commands and responses. The text commands offer the added convenience that at the end of the exchange the value selected is known to both parties. 3.1 SCSI Disconnect-Reconnect Mode Page use in iSCSI The following outlines the SCSI Disconnect-Reconnect mode page usage for iSCSI: Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|P|0| 0x02 | 0x0e | Reserved(0) | +---------------+---------------+---------------+---------------+ 4| Reserved (0) | +---------------+---------------+---------------+---------------+ 8| Reserved (0) | MaximumBurstSize | +---------------+---------------+---------------+---------------+ 12|E| Reserved (0) | FirstBurstSize | +---------------+---------------+---------------+---------------+ 3.1.1 MaximumBurstSize Field (16 bit) This field is used by iSCSI to define the maximum data payload in iSCSI data PDUs or as immediate data in command PDUs in units of 512 bytes. This value can also be set by a text-mode key=value pair (DataPDULength). 3.1.2 E - Enable Modify Data Pointers Bit (EMDP) This field is used to control data ordering within a sequence (unsolicited output, fulfilling an R2T or all the input data). Data PDUs can be in any order (EMDP = 1) or at continuously increasing addresses (EMDP = 0). EMDP can also be set by a text-mode key=value pair (DataOrder). 3.1.3 FirstBurstSize Field (16 bit) Satran, J. Standards-Track, Expire November 2001 76 iSCSI April 19, 2001 This field is used by iSCSI to define the maximum amount of unsolicited data an iSCSI initiator is allowed to send to the target in units of 512 bytes. This value can also be set by a text-mode key=value pair (FirstBurstSize). 3.1.4 Other Fields No other fields in this page are used by iSCSI. 3.2 iSCSI Logical Unit Control Mode Page The following outlines the iSCSI Port mode page: Satran, J. Standards-Track, Expire November 2001 77 iSCSI April 19, 2001 Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|P|0| 0x18 | 0x02 | 0 | iSCSI | Reserved (0)|C| +---------------+---------------+---------------+---------------+ 3.2.1 Enable CRN (C) When this field is set to 1 the CRN field is considered by LU. This field is LU specific and can be set only through the SCSI Mode Set. 3.3 iSCSI Port Mode Page The following outlines the iSCSI Port mode page: Satran, J. Standards-Track, Expire November 2001 78 iSCSI April 19, 2001 Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0|P|0| 0x19 | 0x06 |Rsvd(0)| iSCSI | Reserved (0)|A| +---------------+---------------+---------------+---------------+ 4| LogoutLoginMinTime | LogoutLoginMaxTime | +---------------+---------------+---------------+---------------+ 3.3.1 Protocol Identifier (iSCSI) This field is set to the iSCSI code set by T10 (xx) 3.3.2 Enable ACA (A) When this field is set to 1 the target is mandated to enter ACA state as specified. When set to 0 the target shall not enter ACA state. This field can also be set by a text-mode key=value pair (EnableACA). 3.3.3 LogoutLoginMinTime Minimum time in seconds from a logout or disconnect asynchronous message after which an initiator may attempt a login. This value is returned also as parameter2 in an asynchronous disconnect message. LogoutLoginMinTime can also be negotiated through the corresponding key=value pair in a text command. 3.3.4 LogoutLoginMaxTime Maximum time in seconds after logout or disconnect asynchronous message up to which recovery actions can be attempted (resources are maintained by targets). This value is returned also as parameter3 in an asynchronous disconnect message. LogoutLoginMaxTime can also be negotiated through the corresponding key=value pair in a text command. Satran, J. Standards-Track, Expire November 2001 79 iSCSI April 19, 2001 4. Login Phase In the rest of this chapter, whenever we mention security we mean security and/or data integrity. The login phase establishes an iSCSI session between initiator and target. It sets the iSCSI protocol parameters, security parameters, and authenticates the initiator and target to each other. Operational parameters MAY be negotiated within or outside (after) the login phase. Security MUST be completely negotiated within the Login Phase or provided by external means (e.g., IPSec). In some environments, a target or an initiator is not interested in authenticating its counterpart. It is possible to bypass authentication through the Login Command and Response. The initiator and target MAY want to negotiate authentication and data integrity parameters. Once this negotiation is completed, the channel is considered secure. Authentication and a Secure Channel setup MAY be performed independent of iSCSI (as when using tunneling IPSec or some implementations of transport IPSec) in which case the Login phase can be reduced to operational parameter negotiations. The login phase is implemented via login and text commands and responses only. The login command is sent from the initiator to the target in order to start the login phase. The login response is sent from the target to the initiator to conclude the login phase. Text PDUs are used to implement negotiation, establish security, and set operational parameters. The whole login phase is considered as a single task and has a single Initiator Task Tag (similar to the linked SCSI commands). The login phase sequence of commands and responses proceeds as follows: - Login command (mandatory) - Login Partial-Response (optional) - Text Command(s) and Response(s) (optional) - Login Final-Response (mandatory) Satran, J. Standards-Track, Expire November 2001 80 iSCSI April 19, 2001 The Login Final-response accepts or rejects the Login Command. The Login Final-Response that accepts a Login Command can come only as a response to a Login command with the F bit set to 1 or a Text Command with the F bit set to 1. 4.1 Login Phase Start The login phase starts with a login request via a login command from the initiator to the target. The login request includes: -Protocol version supported by the initiator (currently 0x'01') -Session and connection Ids -Security/Integrity Parameters OR -iSCSI operational parameters A target MAY use the iSCSI Initiator Name as part of its access control mechanism; therefore, the iSCSI Initiator Name MUST be sent before the target is required to disclose its LUs. If the iSCSI Target Name is going to be used in determining the security mode or it is implicit part of authentication, then the iSCSI Target Name MUST be sent in the login command of the first connection of a session to identify the storage endpoint of the session. However, it is OPTIONAL for all the connections after the first. It is ignored by the target for new connections within an existing session. If the iSCSI Target Name is going to be used only for access control, it can be sent after the Security Context Complete is achieved. A unknown target can be accessed by using "iSCSI" as a placeholder for the iSCSI Target Name. The iSCSI Names MUST be in text command format. The target can answer in the following ways: -Login Response with Login Reject (and F bit 1). This is an immediate rejection from the target that causes the session to terminate. -Login Response with Login Accept with session ID and iSCSI parameters and F bit set to 1. This is a valid response only if the Login Command also had the F bit set to 1. In this case, the target does not support any security or authentication mechanism and starts with the session immediately (enters full feature phase). Satran, J. Standards-Track, Expire November 2001 81 iSCSI April 19, 2001 -Login Response with F bit 0 indicating the start of a negotiation sequence. The response includes the protocol version supported by the target and either security/integrity parameters or iSCSI parameters (when no security/integrity mechanism is chosen) supported by the target. It also indicates what sequence is expected next (security/integrity or iSCSI parameters negotiation). The initiator MAY decide to drop the connection if the sequence is not what it expects (e.g., an initiator that expects a security/integrity sequence and gets a response indicating that iSCSI parameters negotiation is the next phase expected by the initiator). 4.2 iSCSI Security and Integrity Negotiation The security exchange sets the security mechanism and authenticates the user and the target to each other. The exchange proceeds according to the algorithms that were chosen in the negotiation phase and is conducted by the text commands key=value parameters. The negotiable security mechanisms include the following modes: -Initiator-target authentication - the host and the target authenticate themselves to each other. A negotiable algorithm such as Kerberos provides this feature. -PDU integrity - an integrity/authentication digest is attached to each packet. The algorithm is negotiable. Using IPsec for encryption or authentication may eliminate the need for security negotiation at the iSCSI level, e.g., ISAKMP for IPsec. If security is established in the login phase note that: -After the security context negotiation is complete, each iSCSI PDU MUST include the appropriate digest field if any. -The iSCSI parameter negotiation (non-security parameters) SHOULD start only after security is established. This should be performed using text commands. The negotiation proceeds as follows: -The initiator sends a text command with an ordered list of the options it supports for each subject (authentication algorithm, iSCSI parameters and so on). The options are listed in the initiator's order of preference. Satran, J. Standards-Track, Expire November 2001 82 iSCSI April 19, 2001 -The target MUST reply with the first option in the list it supports and is allowed for the specific initiator. The parameters are encoded in UTF8 as key=value. The initiator MAY also send proprietary options. The "none" option, if allowed, MUST be included in the list, which indicates that no algorithm is supported by the target. If security is to be established, the initiator MUST NOT send parameters other than security parameters in the login command. The operational parameters should be negotiated only after security is established at the desired level. When establishing the security context, any operational parameters sent before establishing a secure context MAY be ignored by both the target and the initiator. For a list of security parameters see Appendix A. -Every party in the security negotiation indicates that it has completed building its security context (has all the required information) by sending the key=value pair: SecurityContextComplete=Yes The other party either offers some more parameters or answers with the same: SecurityContextComplete=Yes The party that is ready keeps sending the SecurityContextComplete=Yes pair (in addition to new security parameters if required) until the handshake is complete. If the initiator has been the last to complete the handshake it MUST NOT start sending operational parameters within the same text command; a text response including only SecurityContextComplete=Yes concludes the security sub-phase. If the target has been the last to complete the handshake, the initiator can start the operational parameter negotiation with the next text command; the security negotiation sub-phase ends with the target text response. All PDUs sent after the security negotiation sub phase MUST be built using the agreed security. Satran, J. Standards-Track, Expire November 2001 83 iSCSI April 19, 2001 If the security negotiation fails at the target then the target MUST send the appropriate Login Response PDU. If the security negotiation fails at the initiator, the initiator shall drop the connection. 4.3 Operational Parameter Negotiation During the Login Phase Operational parameter negotiation during the login MAY be done: - starting with the Login command if the initiator does not offer any security/ integrity option - starting immediately after the security/integrity negotiation if the initiator and target perform such a negotiation - starting immediately after the Login response with Final bit 0 if the initiator does offer security/integrity options but the target chose none. Operational parameter negotiation MAY involve several request- response exchanges (login and/or text) always driven by the initiator. The initiator MUST indicate its intent to terminate the negotiation by setting the F bit to 1; the target sets the F bit to 1 on the last response. The last response MUST be the Login Response. If the target responds to a text or Login command with the F bit set to 1, with a text response with the F bit set to 0, or a login response with the text bit set to 0, the initiator must keep sending the text command (even empty) with the F bit set to 1 until it gets the Login Response with the F bit set to 1. A target MUST NOT send more than one Login Response with the F bit set to 0. An initiator MUST send a single Login command per connection, per session. Satran, J. Standards-Track, Expire November 2001 84 iSCSI April 19, 2001 5. Operational Parameter Negotiation Outside the Login Phase Operational parameters MAY be negotiated outside (after) the login phase. Operational parameter negotiation MAY involve several text request- response exchanges always driven by the initiator. The initiator MUST indicate its intent to terminate the negotiation by setting the F bit to 1; the target sets the F bit to 1 on the last response. If the target responds to a text command with the F bit set to 1, with a text response with the F bit set to 0, the initiator must keep sending the text command (even empty) with the F bit set to 1 until it gets the text response with the F bit set to 1. Satran, J. Standards-Track, Expire November 2001 85 iSCSI April 19, 2001 6. iSCSI Error Handling and Recovery For any outstanding SCSI command, it is assumed that iSCSI in conjunction with SCSI at the initiator is able to keep enough information to be able to rebuild the command PDU, and that outgoing data is available (in host memory) for retransmission while the command is outstanding. It is also assumed that at target, incoming data (read data) MAY be kept for recovery or it can be re-read from a device server. It is further assumed that a target will keep the "status & sense" for a command it has executed while the total number of outstanding commands and executed commands does not exceed its limit and status has not been acknowledged. 6.1 Format Errors Explicit violations of the rules stated in this document are format errors. While a session is active, whenever a target receives an iSCSI PDU with a format error, it MUST answer with a Reject iSCSI PDU with a Reason-code of Format Error. It MUST also provide a 2-byte offset of the first offending byte in the rejected PDU. When an initiator receives an iSCSI PDU with a format error, for which it has an outstanding task, it MUST abort the target task and report the error through an appropriate service response (e.g., Target Failure). The exact coding of the service response is outside the scope of this document. 6.2 Digest Errors When a target receives an iSCSI PDU with a header digest error or a payload digest error in an iSCSI PDU, it MUST answer with a Reject iSCSI PDU with a Reason-code of Header-Digest-error or Data-Digest- Error and discard the offending PDU. If the error is a Data-Digest- Error in a Data-PDU, the targets MUST either request retransmission with a R2T or answer with a command response PDU with a response-code of delivery-subsystem-failure and terminate the task. If the target is answering with an error in the command response PDU, it must wait for the target to receive all the data (signaled by a Data PDU with the final bit Set for all outstanding R2Ts) before sending the command response PDU. When an initiator receives an iSCSI PDU with a header digest error, it MUST discard it. When an initiator receives any iSCSI PDU other Satran, J. Standards-Track, Expire November 2001 86 iSCSI April 19, 2001 than a data PDU, with a Data-Digest-Error, and this PDU is part of a task (has an Initiator Task Tag set), it MUST discard the PDU. It MAY restart the task (reissue the command with the same Initiator Task Tag and the X-bit set to 1). If the reissued command is a SCSI command and it implies Read Data (Expected Data Length is not 0), the reissued command also includes the sequence number of the Next Data Packet expected by the initiator (0 if there was no data packet yet). When an initiator receives an iSCSI data PDU with a Data-Digest error, it must discard the PDU and it must either request the missing data PDUs through SNACK or abort the task and terminate the command with an error. 6.3 Sequence Errors When an initiator receives an iSCSI data PDU with an out-of-order DataSN or a SCSI command response PDU with an ExpDataSN implying missing data PDUs it MAY request the missing data PDUs through a data SNACK PDU or handle this case as a connection failure. In its turn, the target MUST either reject the SNACK with a Reject PDU with a reason-code of Data-SNACK-Reject or resend the data PDU. When an initiator receives an iSCSI status PDU with an out-of-order StatSN implying missing responses, it MUST either request the missing response PDUs through a status SNACK or handle this case as a connection failure. The target MUST reissue the missing responses. As a side effect of receiving the missing responses, the initiator may discover missing data PDUs. The initiator MUST NOT acknowledge (either explicitly through ExpStatSN or implicitly through a status SNACK) the received responses until it has completed receiving all the data PDUs of a SCSI command. 6.4 Protocol Errors The authors recognize that mapping framed messages over a "stream" connection, such as TCP, makes the proposed mechanisms vulnerable to simple software framing errors. The introduction of framing mechanisms may be onerous for performance and bandwidth. Command Sequence Numbers and the above mechanisms for connection drop and reestablishment help handle this type of mapping errors. 6.5 Connection Failure iSCSI can keep a session in operation if it is able to keep/establish at least one TCP connection between the initiator and target in a timely fashion. It is assumed that targets and/or initiators recognize a failing connection by either transport level means (TCP), Satran, J. Standards-Track, Expire November 2001 87 iSCSI April 19, 2001 a gap in the command or response stream that is not filled for a long time, or by a failing iSCSI NOP-ping. The latter MAY be used periodically by highly reliable implementations. Initiators and targets MAY also use the keep-alive option on the TCP connection to enable early link failure detection on otherwise idle links. At connection failure, the initiator and target MUST either attempt connection recovery within the session or session recovery. 6.6 Session Errors If all the connections of a session fail and cannot be reestablished in a short time or if initiators detect protocol errors repeatedly, an initiator may choose to terminate a session and establish a new session. It terminates all outstanding requests with a appropriate response before initiating a new session. The target takes the following actions: - Resets the TCP connections (close the session). - Aborts all Tasks in the task set for the corresponding initiator. 6.7 Recovery Levels iSCSI enables the following levels of recovery (in increasing coverage order): - within a task (i.e., without requiring command restart). - within a connection (i.e., without requiring the connection to be rebuilt but perhaps requiring command restart). - within a session (i.e., perhaps requiring connections to be rebuilt and commands to be reissued). - session recovery. The recovery scenarios detailed in the rest of this section are representative rather than exclusive. In every case, they detail the lowest level recovery that MAY be attempted. The implementer is left to decide under which circumstances to raise the recovery level and/or what recovery levels to implement. At all levels, the implementer has the choice of deferring errors to the SCSI initiator (with an appropriate response code), in which case the task, if any, has to be removed from the target and all the side- effects (like ACA) have to be considered. Satran, J. Standards-Track, Expire November 2001 88 iSCSI April 19, 2001 Recovery within a connection and within a task MUST NOT be attempted before the connection is in full feature phase. 6.7.1 Recovery Within-task At the target, the following cases lend themselves to within-task recovery: (1)Lost data PDU - a data PDU may be lost due to a header digest error or a data digest error. In case of a data digest error, the error is recognized immediately, and the target MAY request the missing data through R2T. In case of a header digest error, the target will recognize the missing data either when receiving a subsequent piece out of sequence or by a timeout in completing a sequence (no data or partial-data-and- no-F-bit). In this case, too, the target MAY request the missing data through a R2T. The timeout value to be used by a target is outside the scope of this document. At the initiator, the following cases lend themselves to within-task recovery: (1)Lost data PDU or lost R2T - a data PDU or R2T may be lost due to a header digest error or a data digest error. In case of a data digest error, the error is recognized immediately and the initiator MAY request the missing data through SNACK. In case of a header digest error, the initiator recognizes the missing data or R2T either when receiving a subsequent piece out of sequence or by a timeout in completing a sequence (no status). In this case, the initiator MAY request the missing data or R2T through a SNACK. Note however that an initiator SHOULD not request a missing R2T by a SNACK after a timeout to avoid a race; this action is better left to the target. The timeout value to be used by an initiator is outside the scope of this document. Both the iSCSI target and initiator MAY resort to a more drastic, not-within-task recovery procedure in any of these cases. An initiator MAY reissue a command when missing data or status. Satran, J. Standards-Track, Expire November 2001 89 iSCSI April 19, 2001 An iSCSI target MAY reject a data-SNACK with a reject response of data SNACK rejected. In this case, it MUST terminate the command with an iSCSI command response of SNACK rejected; the task is terminated and no future action is expected at target and initiator. An iSCSI initiator MUST accept a R2T. An iSCSI target on detecting missing data MAY terminate the command with an iSCSI error response of Delivery Subsystem Failure. 6.7.2 Recovery Within-connection At the initiator, the following cases lend themselves to within- connection recovery: (1)Lost iSCSI numbered Response recognized by either receiving it with a data digest error or receiving a Response PDU with a higher StatSN than expected. The initiator MAY request the missing responses through SNACK, in which case the target MUST reissue them. (2)Requests not acknowledged for a long time. Requests are acknowledged explicitly through ExpCmdSN or implicitly by receiving data and/or status. The initiator MAY reissue non- acknowledged commands. The reissued, non-acknowledged commands MUST carry their original CmdSN and the X (retry) flag set to 1. Note that this is the only case in which the reissued command carries the same CmdSN as the "original". N.B. While the original connection for a command is still "active" (i.e., has not been logged-out or restarted), any command MUST be retried only on the original connection. After logging out the original connection, commands can be retried on a different connection, but MUST still carry the original CmdSN. At the target, the following cases lend themselves to within- connection recovery: (1)Status/Response not acknowledged for a long time. The target MAY issue a NOP-IN, with the P bit set to 1 or 0, which indicates in the StatSN field the next status number it is going to issue. This helps the initiator detect missing StatSN and issue a SNACK-status. The time to timeout by both initiator and target are outside the scope of this document. Satran, J. Standards-Track, Expire November 2001 90 iSCSI April 19, 2001 Both the iSCSI target and initiator MAY resort to a more drastic, not-within-connection recovery procedure in any of those cases. 6.7.3 Recovery Within-session At an iSCSI initiator, the following cases lend themselves to within session recovery: (1)TCP connection failure. The initiator MUST close the connection following which it MUST either Logout the failed connection, or Login with an implied Logout, and reissue all commands associated with the failed connection on another connection (that MAY be a newly established connection) with the X (retry) flag set to 1. N.B. The logout function is mandatory, while a new connection establishment is mandatory only if the failed connection was the last or only connection in the session N.B. As an alternative to Logout and reissue commands, the initiator MAY instead reset the target and terminate all outstanding commands with a service response indicating Delivery Subsystem Failure. The initiator MUST perform one of the two actions. (2)Receiving an Asynchronous Message requiring recovery Logout. The initiator MUST handle it as a TCP connection failure for the connection referred to in the PDU. At an iSCSI target, the following cases lend themselves to within- session recovery (1)TCP connection failure. The target MUST close the connection and then, if more than one connection is available, the target SHOULD send an Asynchronous Message indicating it has dropped the connection. Following that, the target will wait for the initiator to continue recovery. 6.7.4 Negotiation Recovery Text command and response sequences when used to set/negotiate operational parameters do the negotiation/parameter setting atomically - i.e. either the whole sequence succeeds or no parameter setting takes place. 6.7.5 Session Recovery Satran, J. Standards-Track, Expire November 2001 91 iSCSI April 19, 2001 Session recovery is to be performed when all other recovery attempts have failed. Very simple initiators and targets MAY perform session recovery on all iSCSI errors and therefore place the burden of recovery on the SCSI layer and above. Session recovery implies closing of all TCP connections, aborting at target all executing and queued tasks for the given initiator, terminating at initiator all outstanding SCSI commands with an appropriate SCSI service response and restarting a session on a new connection set (TCP connection establishment and login on all new connections). Satran, J. Standards-Track, Expire November 2001 92 iSCSI April 19, 2001 7. Notes to Implementers This section notes some of the performance and reliability considerations of the iSCSI protocol. This protocol was designed to allow efficient silicon and software implementations. The iSCSI tag mechanism was designed to enable RDMA at the iSCSI level or lower. The guiding assumption made throughout the design of this protocol was that targets are resource constrained relative to initiators. 7.1 Multiple Network Adapters The iSCSI protocol allows multiple connections, not all of which need go over the same network adapter. If multiple network connections are to be utilized with hardware support, the iSCSI protocol command- data-status allegiance to one TCP connection insure that there is no need to replicate information across network adapters or otherwise require them to cooperate. However, some task management commands may require some loose form of cooperation or replication at least on the target. 7.2 Autosense and Auto Contingent Allegiance (ACA) Autosense refers to the automatic return of sense data to the initiator in case a command did not complete successfully. iSCSI mandates support for autosense. ACA helps preserve ordered command execution in presence of errors. As iSCSI can have many commands in-flight between initiator and target iSCSI mandates support for ACA. 7.3 Task Management Commands and Immediate Delivery Task management command may reach the target and, in the case immediate delivery was requested, be executed before all of the tasks it was meant to act upon have been delivered or even reached the target. I will assume that, while pending delivery from iSCSI to SCSI at the target, commands are kept in an iSCSI queue at both the initiator and the target and that the target queue contains both commands and "holes" (placeholders for commands not received yet). The following general mechanism can be used to achieve the effect of ordered delivery for task management commands while enabling the Satran, J. Standards-Track, Expire November 2001 93 iSCSI April 19, 2001 "urgent" delivery that some of them imply and immediate execution of the task management commands without: At Initiator when a relevant task management command is issued: a) if ExpCmdSN is equal to CmdSN skip to step c b) mark all pending commands with a CmdSN field between ExpCmdSN and the current CmdSN and a relevant LUN as candidates for cleanup and retain CmdSN in a "barrier list". c) send the task management command for immediate delivery to the target At initiator when updating ExpCmdSN: a) if the "barrier list" is empty or ExpCmdSN is less than the first entry in the barrier list then skip to step d b) remove the barrier list entry and remove and drop all entries marked for cleanup having a CmdSN field less than ExpCmdSN c) go to step a d) release all queued entries between the old and new ExpCmdSN from the queue At target when receiving a relevant task management command for immediate delivery: a) if ExpCmdSN is equal to CmdSN skip to step c b) mark all pending entries (commands received and placeholders) with a CmdSN field between ExpCmdSN and the current CmdSN as candidates for cleanup and retain CmdSN in a "barrier list" including the referenced LUN (or an ALL marker) c) send the task management command to SCSI for immediate execution At target when updating ExpCmdSN (releasing ordered commands to SCSI): a) if the "barrier list" is empty or ExpCmdSN is less than the first entry in the barrier list then skip to step d b) remove the barrier list entry and remove and drop all entries marked for cleanup and having the same LUN as the barrier entry (any if the barrier is marked ALL) and a CmdSN field less than ExpCmdSN c) go to step a Satran, J. Standards-Track, Expire November 2001 94 iSCSI April 19, 2001 d) release all queued entries between the old and new ExpCmdSN from the queue Note that this scheme will withstand connection recovery. Satran, J. Standards-Track, Expire November 2001 95 iSCSI April 19, 2001 Appendix A. Satran, J. Standards-Track, Expire November 2001 96 iSCSI April 19, 2001 8. Security Considerations Historically, native storage systems have not had to consider security because their environments offered minimal security risks. That is, these environments consisted of storage devices either directly attached to hosts or connected via a subnet distinctly separate from the communications network. The use of storage protocols, such as SCSI, over IP networks requires that security concerns be addressed. iSCSI implementations MUST provide means of protection against active attacks (pretending as another identity, message insertion, deletion, and modification) and MAY provide means of protection against passive attacks (eavesdropping, gaining advantage by analyzing the data sent over the line). The following section describes the security protection modes to be provided by an iSCSI implementation. Authentication and a Secure Channel setup MAY be performed independent of iSCSI (as when using tunneling IPSec or some implementations of transport IPSec). 8.1 iSCSI Security Protection Modes 8.1.1 No Security This mode does not authenticate nor does it encrypt data. This mode should only be used in environments where the security risk is minimal and configuration errors are improbable. 8.1.2 Initiator-Target Authentication In this mode, the target authenticates the initiator and the initiator optionally authenticates the target. An attacker should not gain any advantage by inspecting the authentication phase PDUs (i.e., sending "clear password" is out of the question). This mode protects against an unauthorized access to storage resources by using a false identity (spoofing). Once the authentication phase is completed, all PDUs are sent and received in clear. This mode should only be used when there is minimal risk to man-in-the-middle attacks, eavesdropping, message insertion, deletion, and modification. 8.1.3 Data Integrity and Authentication This mode provides origin authentication and data integrity for every PDU that is sent after a security context is established. It protects Satran, J. Standards-Track, Expire November 2001 97 iSCSI April 19, 2001 against man-in-the-middle attacks, message insertion, deletion, and modification. It is possible to use different authentication mechanisms for headers and data. Every compliant iSCSI initiator and target MUST be able to provide initiator-target authentication and data integrity and authentication. This quality of protection MAY be achieved on every connection through properly configured IPSec involving only administrative (indirect) interaction with iSCSI implementations. 8.1.4 Encryption This mode provides data privacy in addition to data integrity and authentication, and protects against eavesdropping, man-in-the-middle attacks, message insertion, deletion, and modification. A connection or multiple connections MAY be protected end-to-end or partial-path (gateway tunneling) by using IPSec. Satran, J. Standards-Track, Expire November 2001 98 iSCSI April 19, 2001 9. IANA Considerations There will be a well-known port for iSCSI connections. This well- known port will be registered with IANA. Satran, J. Standards-Track, Expire November 2001 99 iSCSI April 19, 2001 10. References and Bibliography [AC] A Detailed Proposal for Access Control, Jim Hafner, T10/99-245 [BOOT] P. Sarkar & team draft-ietf-ips-iscsi-boot-01.txt [CAM] ANSI X3.232-199X, Common Access Method-3 (Cam-3) [Castagnoli93] Guy Castagnoli, Stefan Braeuer and Martin Herrman "Optimization of Cyclic Redundancy-Check Codes with 24 and 32 Parity Bits", IEEE Transact. on Communications, Vol. 41, No. 6, June 1993 [CRC] ISO 3309, High-Level Data Link Control (CRC 32) [NDT] M. Bakke & team, draft-ietf-ips-iSCSI- NamingAndDiscovery-00.txt [RFC793] Transmission Control Protocol, RFC 793 [RFC1122] Requirements for Internet Hosts-Communication Layer RFC1122, R. Braden (editor) [RFC1510] J. Kohl, C. Neuman, "The Kerberos Network Authentication Service (V5)", September 1993. [RFC1766] Alvestrand, H., "Tags for the Identification of Languages", March 1995. [RFC1964] J. Linn, "The Kerberos Version 5 GSS-API Mechanism", June 1996. [RFC1982] Elz, R., Bush, R., "Serial Number Arithmetic", RFC 1982, August 1996. [RFC1994] "W. Simpson, PPP Challenge Handshake Authentication Protocol (CHAP)", RFC 1994, August 1996. [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 3", RFC 2026, October 1996. [RFC2044] Yergeau, F., "UTF-8, a Transformation Format of Unicode and ISO 10646", October 1996. [RFC2119] Bradner, S. "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2025] C. Adams, "The Simple Public-Key GSS-API Mechanism (SPKM)", October 1996. [RFC2234] D. Crocker, P. Overell Augmented BNF for Syntax Specifications: ABNF [RFC2434] T. Narten, and H. Avestrand, "Guidelines for Writing an IANA Considerations Section in RFCs.", RFC2434, October 1998. [RFC2401] S. Kent, R. Atkinson, " Security Architecture for the Internet Protocol", RFC 2401, November 1998 [RFC2945], Wu, T., "The SRP Authentication and Key Exchange System", September 2000. [SAM2] ANSI X3.270-1998, SCSI-3 Architecture Model (SAM-2) [SBC] ANSI X3.306-199X, SCSI-3 Block Commands (SBC) [SCSI2] ANSI X3.131-1994, SCSI-2 Satran, J. Standards-Track, Expire November 2001 100 iSCSI April 19, 2001 [Schneier] Schneier, B., "Applied Cryptography: Protocols, Algorithms, and Source Code in C", 2nd edition, John Wiley & Sons, New York, NY, 1996. [SPC] ANSI X3.301-199X, SCSI-3 Primary Commands (SPC) Satran, J. Standards-Track, Expire November 2001 101 iSCSI April 19, 2001 11. Author's Addresses Julian Satran Kalman Meth Ofer Biran IBM, Haifa Research Lab MATAM - Advanced Technology Center Haifa 31905, Israel Phone +972 4 829 6211 Email: Julian_Satran@vnet.ibm.com meth@il.ibm.com biran@il.ibm.com Daniel F. Smith IBM Almaden Research Center 650 Harry Road San Jose, CA 95120-6099, USA Phone: +1 408 927 2072 Email: dfsmith@almaden.ibm.com Costa Sapuntzakis Cisco Systems, Inc. 170 W. Tasman Drive San Jose, CA 95134, USA Phone: +1 408 525 5497 Email: csapuntz@cisco.com Randy Haagens Hewlett-Packard Company 8000 Foothills Blvd. Roseville, CA 95747-5668, USA Phone: +1 (916) 785-4578 E-mail: Randy_Haagens@hp.com Matt Wakeley Agilent Technologies 1101 Creekside Ridge Drive Suite 100, M/S RH21 Roseville, CA 95661 Phone: +1 (916) 788-5670 E-Mail: matt_wakeley@agilent.com Efri Zeidner SANGate Israel efri@sangate.com Satran, J. Standards-Track, Expire November 2001 102 iSCSI April 19, 2001 Paul von Stamwitz (current address) TrueSAN Networks, Inc. Phone: +1(408)869-4219 E-mail: pvonstamwitz@truesan.com Luciano Dalle Ore Quantum Corp. Phone: +1(408) 232 6524 E-mail: ldalleore@snapserver.com Mallikarjun Chadalapaka Hewlett-Packard Company 8000 Foothills Blvd. Roseville, CA 95747-5668, USA Phone: +1 (916) E-mail: cbm@rose.hp.com Yaron Klein SANRAD 24 Raul Valenberg St. Tel-Aviv, 69719 Israel Phone: +972-3-7659998 E-mail: klein@sanrad.com Comments may be sent to Julian Satran Satran, J. Standards-Track, Expire November 2001 103 iSCSI April 19, 2001 Appendix B. iSCSI Security and Integrity 01 Security Keys and Values The parameters (keys) negotiated for security are: - Digests (HeaderDigest, DataDigest) - Authentication method (AuthMethod) Digests enable checking end-to-end data integrity beyond the integrity checks provided by the link layers and covering the whole communication path including all elements that may change the network level PDUs like routers, switches, proxies etc. The following table lists cyclic integrity checksums that can be negotiated for the digests and MUST be implemented by every iSCSI initiator and target. Note that these digest options have only error detection significance. +---------------------------------------------+ | Name | Description | +---------------------------------------------+ | crc-32C | 32 bit CRC | 11EDC6F41 | +---------------------------------------------+ | none | no digest | +---------------------------------------------+ The generator polynomials for those digests are given in hex- notation, for example 3a stands for 0011 1010 - the polynomial x**5+X**4+x**3+x+1. The generator polynomial selected is evaluated in [Castagnioli93]. Implementations MAY also negotiate digests with security significance for data authentication and integrity as detailed in the following table: Satran, J. Standards-Track, Expire November 2001 104 iSCSI April 19, 2001 +-------------------------------------------------------------+ | Name | Description | Definition | +-------------------------------------------------------------+ | KRB5_MD5 | the SGN_CKSUM field (8 bytes) | RFC1964 | | | of the GSS_GetMIC() token in | | | | GSS_KRB5_INTEG_C_QOP_MD5 QOP | | | | (partial MD5 ("MD2.5") ) | | +-------------------------------------------------------------+ | KRB5_DES_MD5 | the SGN_CKSUM field (8 bytes) | RFC1964 | | | of the GSS_GetMIC() token in | | | | GSS_KRB5_INTEG_C_QOP_DES_MD5 | | | | QOP (DES MAC of MD5) | | +-------------------------------------------------------------+ | KRB5_DES_MAC | the SGN_CKSUM field (8 bytes) | RFC1964 | | | of the GSS_GetMIC() token in | | | | GSS_KRB5_INTEG_C_QOP_ DES_MAC | | | | QOP (DES MAC) | | +-------------------------------------------------------------+ | SPKM | the int-cksum field of the | RFC2025 | | | SPKM-MIC token, calculated | | | | without the optional int-alg | | | | and snd-seq fields of the | | | | mic-header (i.e., the default | | | | I-ALG is used, and sequencing | | | | service is not used). | | +-------------------------------------------------------------+ Note: the KRB5_* digests are allowed only when combined with KRB5 authentication method (see below) (i.e., the initiator may offer one of these digests only if it also offers KRB5 as AuthMethod, and the target may respond with one of these digests only if it also responds with KRB5 as the AuthMethod). Similarly, the SPKM digest is allowed only when combined with SPKM-1 or SPKM-2 authentication methods (see below). Other and proprietary algorithms MAY also be negotiated. The none value is the only one that MUST be supported. The following table details authentication methods: Satran, J. Standards-Track, Expire November 2001 105 iSCSI April 19, 2001 +------------------------------------------------------------+ | Name | Description | +------------------------------------------------------------+ | KRB5 | Kerberos V5 | +------------------------------------------------------------+ | SPKM-1 | Simple Public-Key GSS-API Mechanism | +------------------------------------------------------------+ | SPKM-2 | Simple Public-Key GSS-API Mechanism | +------------------------------------------------------------+ | SRP | Secure Remote Password | +------------------------------------------------------------+ | CHAP | Challenge Handshake Authentication Protocol| +------------------------------------------------------------+ | none | No authentication | +------------------------------------------------------------+ KRB5 is defined in [RFC1510], SPKM-1, SPKM-2 are defined in [RFC2025], Secure Remote Password is defined in [RFC2945] and CHAP is defined in [RFC1994]. 02 Authentication The authentication exchange authenticates the initiator to the target, and optionally the target to the initiator. Authentication is not mandatory and is distinct from the data integrity exchange. The authentication methods to be used are KRB5, SPKM-1, SPKM-2, SRP, CHAP, or proprietary. For KRB5 (Kerberos V5) [RFC1510], the initiator MUST use: KRB_AP_REQ= where KRB_AP_REQ is the client message as defined in [RFC1510]. If the initiator authentication fails, the target MUST return an error. Otherwise, if the initiator has selected the mutual authentication option (by setting MUTUAL-REQUIRED in the ap-options field of the KRB_AP_REQ), the target MUST reply with: KRB_AP_REP= where KRB_AP_REP is the server's response message as defined in [RFC1510]. Satran, J. Standards-Track, Expire November 2001 106 iSCSI April 19, 2001 KRB_AP_REQ,KRB_AP_REP are large binaries encoded as hexadecimal strings. For SPKM-1,SPKM-2 [RFC2025], the initiator MUST use: SPKM-REQ= where SPKM-REQ is the first initiator token as defined in [RFC2025]. [RFC2025] defines situations where each side may send an error token which may cause the peer to re-generate and resend his last token. This scheme is followed in iSCSI, and the error token syntax is: SPKM-ERROR= However, SPKM-DEL tokens that are defined by [RFC2025] for fatal errors will not be used by iSCSI. If the target needs (by [RFC2025]) to send SPKM-DEL token, it will, instead, send a Login "login reject" message and terminate the connection. If the initiator needs to send SPKM-DEL token, it will just abort the connection. In the sequel, we assume that no SPKM-ERROR tokens are required: If the initiator authentication fails, the target MUST return an error. Otherwise, if the AuthMethod is SPKM-1 or if the initiator has selected the mutual authentication option (by setting mutual-state bit in the options field of the REQ-TOKEN in the SPKM-REQ), the target MUST reply with: SPKM-REP-TI= where SPKM-REP-TI is the target token as defined in [RFC2025]. If mutual authentication was selected and target authentication fails, the initiator MUST abort the connection. Otherwise, if the AuthMethod is SPKM-1, the initiator MUST continue with: SPKM-REP-IT= where SPKM-REP-IT is the second initiator token as defined in [RFC2025]. All the SPKM-* tokens are large binaries encoded as hexadecimal strings. Satran, J. Standards-Track, Expire November 2001 107 iSCSI April 19, 2001 For SRP [RFC2945], the initiator MUST use: U= TargetAuth=yes /* or TargetAuth=no */ The target MUST either return an error or reply with: N= g= s= The initiator MUST continue with: A= The target MUST either return an error or reply with: B= The initiator MUST either abort or continue with: M= If the initiator authentication fails, the target MUST return an error. Otherwise, If the initiator sent TargetAuth=yes in the first message (requiring target authentication) the target MUST reply with: HM= Where U, N, g, s, A, B, M and H(A | M | K) are defined in [RFC2945]. U is a text string, N,g,s,A,B,M and H(A | M | K) are numbers. For CHAP [RFC1994], the initiator MUST use: A= Where A1,A2... are proposed algorithms, in order of preference. The target MUST either return an error or reply with: A= I= C= Where A is one of A1,A2... that were proposed by the initiator. The initiator MUST continue either with: Satran, J. Standards-Track, Expire November 2001 108 iSCSI April 19, 2001 N= R= or, if he requires target authentication, with: N= R= I= C= If the initiator authentication fails, the target MUST return an error. Otherwise, if the initiator required target authentication, the target MUST reply with N= R= Where N, (A,A1,A2), I, C, R are (correspondingly) the Name, Algorithm, Identifier, Challenge and Response as defined in [RFC1994]. N is a text string, A,A1,A2,I are numbers and C,R are large binaries encoded as hexadecimal strings. For the Algorithm, as stated in [RFC1994], one value is required to be implemented: 5 (CHAP with MD5) To guarantee interoperability, initiators SHOULD always offer it as one of the proposed algorithms. 03 Login Phase Examples In the first example, the initiator and target authenticate each other via Kerberos: I-> Login iSCSI-Initiator-Name=com.os.hostid.77 iSCSI-Target- Name=com.acme.diskarray.sn.88 HeaderDigest=KRB5_MD5,KRB5_DES_MAC,crc-32C,none DataDigest=crc-32C,none AuthMethod=SRP,KRB5,none T-> Login-PR HeaderDigest=KRB5_MD5 DataDigest=crc-32C AuthMethod=KRB5 (Login-PR stands for Login-Partial-Response) I-> Text KRB_AP_REQ= (krb_ap_req contains the Kerberos V5 ticket and authenticator with MUTUAL-REQUIRED set in the ap-options field) If the authentication is successful, the target proceeds with: Satran, J. Standards-Track, Expire November 2001 109 iSCSI April 19, 2001 T-> Text KRB_AP_REP= SecurityContextComplete=Yes (krb_ap_rep is the Kerberos V5 mutual authentication reply) If the authentication is successful, the initiator proceeds: I-> Text SecurityContextComplete=Yes T-> Text SecurityContextComplete=Yes From this point on, any Text command and each PDU thereafter has a KRB5_MD5 digest for the header and a crc-32C for the data. The initiator may proceed: I-> Text ... iSCSI parameters T-> Text ... iSCSI parameters And at the end: I-> Text optional iSCSI parameters F bit set to 1 T-> Login "login accept" iSCSI-Target- Name=com.acme.diskarray.sn.88 If the initiator authentication by the target is not successful, the target responds with: T-> Login "login reject" instead of the Text KRB_AP_REP message, and terminates the connection. If the target authentication by the initiator is not successful, the initiator terminates the connection (without responding to the Text KRB_AP_REP message). In the next example only the initiator is authenticated by the target via Kerberos: I-> Login iSCSI-Initiator-Name=com.os.hostid.77 iSCSI-Target-Name=com.acme.diskarray.sn.88 HeaderDigest=KRB5_MD5,KRB5_DES_MAC,crc-32C,none DataDigest=crc-32C,none AuthMethod=SRP,KRB5,none T-> Login-PR HeaderDigest=KRB5_MD5 DataDigest=crc-32C AuthMethod=KRB5 I-> Text KRB_AP_REQ=krb_ap_req SecurityContextComplete=Yes Satran, J. Standards-Track, Expire November 2001 110 iSCSI April 19, 2001 (MUTUAL-REQUIRED not set in the ap-options field of krb_ap_req) If the authentication is successful, the target proceeds with: T-> Text SecurityContextComplete=Yes From this point on, any Text command and each PDU thereafter MUST have a KRB5_MD5 digest for the header and a crc-32C for the data. I-> Text ... iSCSI parameters T-> Text ... iSCSI parameters . . . T-> Login "login accept" iSCSI-Target- Name=com.acme.diskarray.sn.88 In the next example, the initiator and target authenticate each other via SPKM-1: I-> Login iSCSI-Initiator-Name=com.os.hostid.77 iSCSI-Target- Name=com.acme.diskarray.sn.88 HeaderDigest=KRB5_MD5,KRB5_DES_MAC,SPKM,crc-32C,none DataDigest=crc-32C,SPKM,none AuthMethod=SPKM-1,KRB5,none T-> Login-PR HeaderDigest=SPKM DataDigest=SPKM AuthMethod=SPKM-1 I-> Text SPKM-REQ= (spkm-req is the SPKM-REQ token with the mutual-state bit in the options field of the REQ-TOKEN set) T-> Text SPKM-REP-TI= If the authentication is successful, the initiator proceeds: I-> Text SPKM-REP-IT= SecurityContextComplete=Yes If the authentication is successful, the target proceeds with: T-> Text SecurityContextComplete=Yes From this point on, any Text command and each PDU thereafter has SPKM digests for the header and data. Satran, J. Standards-Track, Expire November 2001 111 iSCSI April 19, 2001 The initiator may proceed: I-> Text ... iSCSI parameters T-> Text ... iSCSI parameters And at the end: I-> Text optional iSCSI parameters F bit set to 1 T-> Login "login accept" iSCSI-Target- Name=com.acme.diskarray.sn.88 If the target authentication by the initiator is not successful, the initiator terminates the connection (without responding to the Text SPKM-REP-TI message). If the initiator authentication by the target is not successful, the target responds with: T-> Login "login reject" instead of the Text SecurityContextComplete=Yes message, and terminates the connection. In the next example, the initiator and target authenticate each other via SPKM-2: I-> Login iSCSI-Initiator-Name=com.os.hostid.77 iSCSI-Target- Name=com.acme.diskarray.sn.88 HeaderDigest=SPKM,crc-32C,none DataDigest=crc-32C,SPKM,none AuthMethod=SPKM-1,SPKM-2,none T-> Login-PR HeaderDigest=SPKM DataDigest=SPKM AuthMethod=SPKM-2 I-> Text SPKM-REQ= SecurityContextComplete=Yes (spkm-req is the SPKM-REQ token with the mutual-state bit in the options field of the REQ-TOKEN not set) If the authentication is successful, the target proceeds with: T-> Text SecurityContextComplete=Yes Satran, J. Standards-Track, Expire November 2001 112 iSCSI April 19, 2001 From this point on, any Text command and each PDU thereafter has SPKM digests for the header and data. The initiator may proceed: I-> Text ... iSCSI parameters T-> Text ... iSCSI parameters And at the end: I-> Text optional iSCSI parameters F bit set to 1 T-> Login "login accept" iSCSI-Target- Name=com.acme.diskarray.sn.88 In the next example, the initiator and target authenticate each other via SRP: I-> Login iSCSI-Initiator-Name=com.os.hostid.77 iSCSI-Target-Name=com.acme.diskarray.sn.88 HeaderDigest=crc- 32C,none DataDigest=crc-32C,none AuthMethod=KRB5,SRP,none T-> Login-PR HeaderDigest=crc-32C DataDigest=crc-32C AuthMethod=SRP I-> Text U= TargetAuth=yes T-> Text N= g= s= I-> Text A= T-> Text B= I-> Text M= If the initiator authentication is successful, the target proceeds: T-> Text HM= SecurityContextComplete=Yes If the target authentication is not successful, the initiator terminates the connection. Otherwise it proceeds: I-> Text SecurityContextComplete=Yes T-> Text SecurityContextComplete=Yes Where N, g, s, A, B, M, and H(A | M | K) are defined in [RFC2945]. From this point on, any Text command and each PDU thereafter has a crc-32C digest for the header and the data. Satran, J. Standards-Track, Expire November 2001 113 iSCSI April 19, 2001 I-> Text ... iSCSI parameters T-> Text ... iSCSI parameters And at the end: I-> Text optional iSCSI parameters and F bit set to 1 T-> Login "login accept" iSCSI-Target- Name=com.acme.diskarray.sn.88 If the initiator authentication is not successful, the target responds with: T-> Login "login reject" Instead of the T-> Text HM= message and terminates the connection. In the next example only the initiator is authenticated by the target via SRP: I-> Login iSCSI-Initiator-Name=com.os.hostid.77 iSCSI-Target-Name=com.acme.diskarray.sn.88 HeaderDigest=crc- 32C,none DataDigest=crc-32C,none AuthMethod=KRB5,SRP,none T-> Login-PR HeaderDigest=crc-32C DataDigest=crc-32C AuthMethod=SRP I-> Text U= TargetAuth=no T-> Text N= g= s= I-> Text A= T-> Text B= I-> Text M= SecurityContextComplete=Yes If the initiator authentication is successful, the target proceeds: T-> Text SecurityContextComplete=Yes From this point on, any Text command and each PDU thereafter has a crc-32C digest for the header and the data. I-> Text ... iSCSI parameters T-> Text ... iSCSI parameters And at the end: I-> Text optional iSCSI parameters and F bit set to 1 Satran, J. Standards-Track, Expire November 2001 114 iSCSI April 19, 2001 T-> Login "login accept" iSCSI-Target- Name=com.acme.diskarray.sn.88 In the next example the initiator and target authenticate each other via CHAP: I-> Login iSCSI-Initiator-Name=com.os.hostid.77 iSCSI-Target-Name=com.acme.diskarray.sn.88 HeaderDigest=crc- 32C,none DataDigest=crc-32C,none AuthMethod=KRB5,CHAP,none T-> Login-PR HeaderDigest=crc-32C DataDigest=crc-32C AuthMethod=CHAP I-> Text A= T-> Text A= I= C= I-> Text N= R= I= C= If the initiator authentication is successful, the target proceeds: T-> Text N= R= SecurityContextComplete=Yes If the target authentication is not successful, the initiator abort the connection. Otherwise it proceeds: I-> Text SecurityContextComplete=Yes T-> Text SecurityContextComplete=Yes From this point on, any Text command and each PDU thereafter has a crc-32C digest for the header and the data. I-> Text ... iSCSI parameters T-> Text ... iSCSI parameters And at the end: I-> Text optional iSCSI parameters and F bit set to 1 T-> Login "login accept" iSCSI-Target- Name=com.acme.diskarray.sn.88 If the initiator authentication is not successful, the target responds with: T-> Login "login reject" Instead of the Text R= SecurityContextComplete=Yes Satran, J. Standards-Track, Expire November 2001 115 iSCSI April 19, 2001 message and terminates the connection. In the next example only the initiator is authenticated by the target via CHAP: I-> Login iSCSI-Initiator-Name=com.os.hostid.77 iSCSI-Target-Name=com.acme.diskarray.sn.88 HeaderDigest=crc- 32C,none DataDigest=crc-32C,none AuthMethod=KRB5,CHAP,none T-> Login-PR HeaderDigest=crc-32C DataDigest=crc-32C AuthMethod=CHAP I-> Text A= T-> Text A= I= C= I-> Text N= R= SecurityContextComplete=Yes If the initiator authentication is successful, the target proceeds: T-> Text SecurityContextComplete=Yes I-> Text ... iSCSI parameters T-> Text ... iSCSI parameters And at the end: I-> Text optional iSCSI parameters and F bit set to 1 T-> Login "login accept" iSCSI-Target- Name=com.acme.diskarray.sn.88 In the next example, the initiator does not offer any security/integrity parameters, so it may offer iSCSI parameters on the Login PDU with the F bit set to 1, and the target may respond with a final Login Response PDU immediately: I-> Login iSCSI-Initiator-Name=com.os.hostid.77 iSCSI-Target-Name=com.acme.diskarray.sn.88 ... iSCSI parameters T-> Login "login accept" iSCSI-Target-Name=com.acme.diskarray.sn.88 ... ISCSI parameters In the next example, the initiator does offer security/integrity parameters on the Login PDU, but the target does not choose any (i.e., chooses the "none" values): Satran, J. Standards-Track, Expire November 2001 116 iSCSI April 19, 2001 I-> Login iSCSI-Initiator-Name=com.os.hostid.77 iSCSI-Target-Name=com.acme.diskarray.sn.88 HeaderDigest=crc- 32C,none DataDigest=crc-32C,none AuthMethod:KRB5,SRP T-> Login-PR I-> Text ... iSCSI parameters T-> Text ... iSCSI parameters And at the end: I-> Text optional iSCSI parameters F bit set to 1 T-> Login "login accept" iSCSI-Target- Name=com.acme.diskarray.sn.88 Note that no SecurityContextComplete=Yes is required since no security mechanism was chosen. Satran, J. Standards-Track, Expire November 2001 117 iSCSI April 19, 2001 Appendix C. Examples 04 Read Operation Example |Initiator Function| PDU Type | Target Function | +------------------+-----------------------+----------------------+ | Command request |SCSI Command (READ)>>> | | | (read) | | | +------------------+-----------------------+----------------------+ | | | Prepare Data Transfer| +------------------+-----------------------+----------------------+ | Receive Data | <<< SCSI Data | Send Data | +------------------+-----------------------+----------------------+ | Receive Data | <<< SCSI Data | Send Data | +------------------+-----------------------+----------------------+ | Receive Data | <<< SCSI Data | Send Data | +------------------+-----------------------+----------------------+ | | <<< SCSI Response |Send Status and Sense | +------------------+-----------------------+----------------------+ | Command Complete | | | +------------------+-----------------------+----------------------+ Satran, J. Standards-Track, Expire November 2001 118 iSCSI April 19, 2001 05 Write Operation Example +------------------+-----------------------+---------------------+ |Initiator Function| PDU Type | Target Function | +------------------+-----------------------+---------------------+ | Command request |SCSI Command (WRITE)>>>| Receive command | | (write) | | and queue it | +------------------+-----------------------+---------------------+ | | | Process old commands| +------------------+-----------------------+---------------------+ | | | Ready to process | | | <<< R2T | WRITE command | +------------------+-----------------------+---------------------+ | Send Data | SCSI Data >>> | Receive Data | +------------------+-----------------------+---------------------+ | | <<< R2T | | +------------------+-----------------------+---------------------+ | | <<< R2T | | +------------------+-----------------------+---------------------+ | Send Data | SCSI Data >>> | Receive Data | +------------------+-----------------------+---------------------+ | Send Data | SCSI Data >>> | Receive Data | +------------------+-----------------------+---------------------+ | | <<< SCSI Response |Send Status and Sense| +------------------+-----------------------+---------------------+ | Command Complete | | | +------------------+-----------------------+---------------------+ Satran, J. Standards-Track, Expire November 2001 119 iSCSI April 19, 2001 Appendix D. Synch and Steering with Fixed Interval Markers This appendix presents a simple scheme for synchronization (PDU boundary retrieval). It uses markers including synchronization information placed at fixed intervals in the TCP stream. A Marker consists of: Byte / 0 | 1 | 2 | 3 | / | | | | |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0| +---------------+---------------+---------------+---------------+ 0| Next-iSCSI-PDU-start pointer - copy #1 | +---------------+---------------+---------------+---------------+ 4| Next-iSCSI-PDU-start pointer - copy #2 | +---------------+---------------+---------------+---------------+ The Marker indicates the offset to the next iSCSI PDU header. The Marker is eight bytes in length, and contains two 32-bit offset fields that indicate how many bytes to skip in the TCP stream in order to find the next iSCSI PDU header. The offset is counted from the marker end to the beginning of the next header. The marker uses two copies of the pointer so that a marker spanning a TCP packet boundary should leave at least one valid copy in one of the packets. The use of markers is negotiable. The initiator and target MAY indicate their readiness to receive and/or send markers during login separately for each connection. The default is NO. In certain environments a sender not willing to supply markers to a receiver willing to accept markers MAY suffer from a considerable performance degradation. Satran, J. Standards-Track, Expire November 2001 120 iSCSI April 19, 2001 06 Markers At Fixed Intervals At fixed intervals in the TCP byte stream, a marker is inserted. Each end of the iSCSI session specifies during login the interval at which it is willing to receive the marker or disables the marker altogether. If a receiver indicates that it desires a marker, the sender SHOULD agree (during negotiation) and provide the marker at the desired interval. The marker interval and the initial marker-less interval are counted in terms of the TCP stream data. Anything counted in the TCP sequence-number is counted for the interval and the initial marker- less interval. Specifically this includes any bytes "inserted" in the TCP stream by an UFL. When reduced to iSCSI terms markers MUST indicate the offset to a 4- byte word boundary in the stream. The last 2 bits of each marker word are reserved and are considered 0 for offset computation. Padding iSCSI PDU payloads to 4-byte word boundaries simplifies marker manipulation. 07 Initial Marker-less Interval To enable the connection setup including the login phase negotiation, the negotiated marking is started at a negotiated boundary in the stream. The marker-less interval is not less than 4 kbytes and the default is 4 kbytes. Satran, J. Standards-Track, Expire November 2001 121 iSCSI April 19, 2001 Appendix E. Login/Text Miscellaneous Keys ISID and TSID form collectively the SSID (session id). A TSID of zero indicates a leading connection. Some session specific parameters MUST be carried only on the leading connection and cannot be changed after the leading connection login(e.g., MaxConnections, the maximum immediate data length requested). This holds even for a single connection session during connection restart. The keys that fall into this category have the use defined as LO (Leading Only). Key that can be used only during login have the use defined as IO (initialize only) while those that can be used in both the login phase and full feature phase have the use defined as ALL. Unless explicitly stated otherwise, all key=value pairs specified here are session specific. 08 MaxConnections Use: LO Who: Initiator and Target MaxConnections= Default is 8. Initiator and target negotiate the maximum number of connections requested/acceptable. The lower of the 2 numbers is selected. 09 TargetName Use: LO by initiator ALL by target Who: Initiator and Target TargetName= Examples: TargetName=com.disk-vendor.diskarrays.sn.45678 TargetName=eui.020000023B040506 TargetName=oui.00023B.target.45 TargetName=iSCSI Satran, J. Standards-Track, Expire November 2001 122 iSCSI April 19, 2001 This key MUST be provided by the initiator of the TCP connection to the remote endpoint before the end of the login phase. The iSCSI Target Name specifies the worldwide unique name of the target. The non-unique default name "iSCSI" may be used to indicate whatever default target exists at the address to which the connection was made. Some targets MAY require this key before authenticating. The TargetName key may also be returned by the "SendTargets" text command, described in detail in [NDT]. 10 InitiatorName Use: LO Who: Initiator and Target InitiatorName= Examples: InitiatorName=com.os-vendor.plan9.cdrom.12345 InitiatorName=com.service-provider.users.customer235.host90 InitiatorName=iSCSI This key MUST be provided by the initiator of the TCP connection to the remote endpoint before the end of the login phase. The Initiator key enables the initiator to identify itself to the remote endpoint. The use of the group name "iSCSI" is interpreted as "other side of TCP connection". The target may silently ignore this key if it does not support it, and does not need to track or verify which initiators use it. A target that supports this field may use it to allow or deny access to an initiator. 11 TargetAlias Use: ALL Who: Target TargetAlias= Examples: TargetAlias=Bob's Disk TargetAlias=Database Server 1 Log Disk TargetAlias=Web Server 3 Disk 20 If a target has been configured with a human-readable name or description, this name MUST be communicated to the initiator during a Satran, J. Standards-Track, Expire November 2001 123 iSCSI April 19, 2001 Login Response PDU. This string is not used as an identifier, but can be displayed by the initiator's user interface in a list of targets to which it is connected. This field MUST also be returned in the response to the "SendTargets" text command if it is set at the target. 12 InitiatorAlias Use: ALL Who: Initiator InitiatorAlias= Examples: InitiatorAlias=Web Server 4 InitiatorAlias=spyalley.nsa.gov InitiatorAlias=Exchange Server If an initiator has been configured with a human-readable name or description, it may be communicated to the target during a Login Request PDU. If not, the host name can be used instead. This string is not used as an identifier, but can be displayed by the target's user interface in a list of initiators to which it is connected. This key SHOULD be sent by an initiator within the Login phase if available. 13 TargetAddress Use: ALL Who: Target TargetAddress=domainname[:port]/iSCSI-Name N.B. If the address contains a iSCSI-Name part then this is a LO parameter. Examples: TargetAddress=10.0.0.1/com.disk-vendor.diskarrays.sn.45678 TargetAddress=12.5.7.10.0.0.1/com.gateways.yourtargets.24 TargetAddress=computingcenter.acme.com/com.disk- vendor.diskarrays.sn.45678 Satran, J. Standards-Track, Expire November 2001 124 iSCSI April 19, 2001 The response to a SendTargets text command returns one or more target addresses for each iSCSI Target Name it returns. This field is used to indicate one of the known addresses of the target. If the list can't be delivered, as a single text response PDU, several lists can be sent using several text response PDUs and the list perceived by the initiator is a logical merge of the individual lists. 14 SendTargets Use: ALL Who: Initiator This key is used within a text command to request a list of targets be sent back to the initiator in a text response. The presence of this key is sufficient to do this; no value should be sent with this key. Example: SendTargets= 15 AccessID Use: ALL Who: Initiator AccessID= Deliver a SCSI AccessID to the target 16 FMarker Use: IO Who: Initiator and Target FMarker= This is a connection specific parameter. Examples: I->FMarker=send-receive T->FMarker=send-receive results in Marker being used in both directions while Satran, J. Standards-Track, Expire November 2001 125 iSCSI April 19, 2001 I->FMarker=send-receive T->FMarker=receive results in Marker being used from the initiator to the target but not from the target to initiator. 17 RFMarkInt Use: IO Who: Initiator and Target RFMarkInt=[,] This is a connection specific parameter. The receiver indicates the minimum to maximum interval (in 4-byte words) the receiver wants the markers. In case the receiver wants only a specific value, only a single value has to be specified. The sender selects a value within the minimum and maximum the receiver requires (or the only value the receiver requires) or indicates through the FMarker key=value its inability to set markers. The interval is measured from the end of a marker to the beginning of the next marker. For example, a value of 1024 means 1024 words (4096 bytes of "pure" payload between markers). Default is 2048. 18 SFMarkInt Use: IO Who: Initiator and Target SFMarkInt= This is a connection specific parameter. Indicates at what interval (in 4-byte words) the sender accepts to send the markers. The number MUST be within the range required by the receiver. The interval is measured from the end of a marker to the beginning of the next marker. For example, a value of 1024 means 1024 words (4096 bytes of "pure" payload between markers). Default is 2048. Satran, J. Standards-Track, Expire November 2001 126 iSCSI April 19, 2001 19 IFMarkInt Use: IO Who: Initiator and Target IFMarkInt= This is a connection specific parameter. Indicates the initial marker-less interval required by the initiator in both directions in 4-byte words. The interval is measured from the beginning of the TCP stream to the beginning of the first marker. For example, a value of 1024 means 1024 words (4096 bytes of "pure" payload up to the first marker). Default value is 1024. 20 InitialR2T Use: ALL Who: Initiator and Target InitialR2T= Examples: I->InitialR2T=no T->InitialR2T=no Default is yes. The InitialR2T key is used to turn off the default use of R2T, thus allowing an initiator to start sending data to a target as if it has received an initial R2T with Buffer Offset=0 and Desired Data Transfer Length=min (FirstBurstSize, Expected Data Transfer Length). The default action is that R2T is required, unless both the initiator and the target send this key-pair attribute specifying InitialR2T=no. Once InitialR2T has been set to 'no', it cannot be set back to 'yes'. Note that only the first outgoing data item (either immediate data or a separate PDU) can be sent unsolicited by a R2T. 21 BidiInitialR2T Use: ALL Who: Initiator and Target Satran, J. Standards-Track, Expire November 2001 127 iSCSI April 19, 2001 BidiInitialR2T= Examples: I->BidiInitialR2T=no T->BidiInitialR2T=no The BidiInitialR2T key is used to turn off the default use of BiDiR2T, thus allowing an initiator to send data to a target without the target having sent a R2T to the initiator for the output data (write part) of a Bi-directional command (having both the R and the W bits set). The default action is that R2T is required, unless both the initiator and the target send this key-pair attribute specifying BidiInitialR2T=no. Once BidiInitialR2T has been set to 'no', it cannot be set back to 'yes'. Note that only the first outgoing data burst (immediate data or separate PDUs) can be sent unsolicited by a R2T. 22 ImmediateData Use: ALL Who: Initiator and Target ImmediateData= Default is yes. Initiator and target negotiate support for immediate data. If ImmediateData is set to yes and InitialR2T is set to yes (default) then only immediate data are accepted in the first burst. If ImmediateData is set to no and InitialR2T is set to yes then the initiator MUST NOT send unsolicited data and the target MUST reject them with the corresponding response code. If ImmediateData is set to no and InitialR2T is set to no then the initiator MUST NOT send unsolicited immediate data but MAY send one unsolicited burst of Data-OUT PDUs. If ImmediateData is set to yes and InitialR2T is set to yes then the initiator MAY send unsolicited immediate data or one unsolicited burst of Data-OUT PDUs but MUST NOT send both immediate and a unsolicited burst of Data-OUT PDUs for any one command. The following table is a summary of unsolicited data options: Satran, J. Standards-Track, Expire November 2001 128 iSCSI April 19, 2001 +----------+-------------+--------------------------------------+ |InitialR2T|ImmediateData| Result (up to FirstBurstSize) | +----------+-------------+--------------------------------------+ | no | no | Unsolicited data in data PDUs only | +----------+-------------+--------------------------------------+ | no | yes | Immediate & separate unsolicited data| | | | but only one of them per command | +----------+-------------+--------------------------------------+ | yes | no | Unsolicited data disallowed | +----------+-------------+--------------------------------------+ | yes | yes | Immediate unsolicited data only | +----------+-------------+--------------------------------------+ 23 DataPDULength Use: ALL Who: Initiator and Target DataPDULength= Default is 16 units. Initiator and target negotiate the maximum data payload supported for command or data PDUs in units of 512 bytes. The minimum of the 2 numbers is selected. This parameter sets the maximum-burst-size value stored in the SCSI disconnect-reconnect mode page. The value can subsequently be retrieved with the mode sense SCSI command. 24 FirstBurstSize Use: ALL Who: Initiator and Target FirstBurstSize= Default is 128 units. Initiator and target negotiate the maximum length supported for unsolicited data in units of 512 bytes. The minimum of the 2 numbers is selected. This parameter sets the first-burst-size value stored in the SCSI disconnect-reconnect mode page. The value can subsequently be retrieved with the mode sense SCSI command. Satran, J. Standards-Track, Expire November 2001 129 iSCSI April 19, 2001 25 LogoutLoginMinTime Use: ALL Who: Initiator and Target LogoutLoginMinTime= Default is 1. Initiator and target negotiate the minimum time in seconds a Login may follow a Logout response or Asynchronous Message announcing disconnect. The maximum of the 2 values is selected. 26 LogoutLoginMaxTime Use: ALL Who: Initiator and Target LogoutLoginMaxTime= Default is 3. Initiator and target negotiate the maximum time in seconds after which recovery is still possible after a logout or Asynchronous Message announcing disconnect. The minimum of the 2 values is selected. 27 EnableACA Use: ALL Who: Initiator and Target EnableACA= Default is yes. Initiator and target negotiate support for ACA. If ACA is not supported by the initiator, it should set the EnableACA to no. A target that does not support ACA answers with no to an attempt by the initiator to set it to yes. This parameter sets the EnableACA field stored in the SCSI Logical Unit Control mode page. Satran, J. Standards-Track, Expire November 2001 130 iSCSI April 19, 2001 28 MaxOutstandingR2T Use: ALL Who: Initiator and Target MaxOutstandingR2T= The default is 8. Initiator and target negotiate the maximum number of outstanding R2Ts per task. 29 DataOrder Use: LO Who: Initiator and Target DataOrder= The default is yes but targets MAY support no. No is used by iSCSI to indicate that the data PDUs can be in any order (EMDP = 1). Yes is used to indicate that incoming data PDUs have to be at continuously increasing addresses (EMDP = 0). This also sets the Connect-Disconnect mode page EMDP bit. 30 BootSession Use: LO Who: Initiator BootSession= Default is no. BootSession MAY be set to yes by the Login Command indicating to the Target that the only purpose of this Session is boot. The target MAY restrict the type of iSCSI requests it accepts in such a Session to Logout, NOP-out, and SCSI read commands. Accepting other commands in this type of session is vendor-dependent. A target MAY reject a boot-session. 31 The Glen-Turner Vendor Specific Key Format Use: ALL Who: Initiator and Target Satran, J. Standards-Track, Expire November 2001 131 iSCSI April 19, 2001 X-reversed.vendor.dns_name.do_something= Keys with this format are used for vendor-specific purposes. These keys always start with X- . To identify the vendor it is suggested to use the reversed DNS-name as a prefix to the key-proper. Satran, J. Standards-Track, Expire November 2001 132 iSCSI April 19, 2001 Full Copyright Statement "Copyright (C) The Internet Society (date). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." Satran, J. Standards-Track, Expire November 2001 133