Network Working Group R. R. Stewart INTERNET-DRAFT M. A. Ramalho Cisco Systems Q. Xie Motorola M. Tuexen Siemens AG I. Rytina Ericsson P. Conrad Temple University expires in six months May 7, 2001 SCTP Dynamic Addition of IP addresses Status of This Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026 [RFC2026]. 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. 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 This document describes extensions to the Stream Control Transmission Protocol (SCTP) [RFC2960] that provide a method to reconfigure IP address information on an existing association or to request that a peer set a stream flow limit. TABLE OF CONTENTS 1. Introduction............................................... 2 2. Conventions................................................ 3 3. Additional Chunks and Parameters........................... 3 3.1 New Chunk Types........................................... 3 3.1.1 Address Configuration Change Chunk (ASCONF)............ 3 3.1.2 Address Configuration Acknowledgment Chunk (ASCONF-ACK) 3.2 New Parameter Types....................................... 4 3.2.1 Add IP Address.......................................... 6 3.2.2 Delete IP Address....................................... 6 3.2.3 Stream Flow Limit Change................................ 7 3.2.4 Error Cause Indication.................................. 7 3.2.5 Set Primary IP Address.................................. 8 Stewart et.al. [Page 1] Internet Draft Address/Stream Configuration May 2001 3.2.6 Success Indication...................................... 8 3.3 New Error Causes.......................................... 9 3.3.1 Error Cause: Request to Delete Last remaining IP Address 9 3.3.2 Error Cause: Operation Refused due to Resource Shortage.10 3.3.3 Error Cause: Request to Delete Source IP Address........10 4. Procedures.................................................11 4.1 ASCONF Chunk Procedures...................................11 4.1.1 Congestion Control of ASCONF Chunks.....................12 4.2 Upon reception of a ASCONF Chunk..........................13 4.3 General rules for address manipulation....................15 4.3.1 A special case for OOTB ABORT chunks....................17 4.4 Setting of the primary address............................18 4.5 Steam Flow Limit Procedures...............................18 4.5.1 Stream Receiver side procedures.........................19 4.5.2 Stream Sender side procedures...........................19 4.5.3 ULP considerations on the use of SCTP flow limit facility................................................20 5. Security Considerations....................................20 6. IANA considerations........................................20 7. Authors' Addresses.........................................20 8. References.................................................21 1. Introduction To extend the utility and application senarios of SCTP, this document introduces optional extensions that provide SCTP with the ability to reconfigure IP address information on an existing association or to request the peer set a stream flow limit. These extensions enable SCTP to be utilized in the following applications: - Dynamic IP addresses added and subtracted extension: For computational or networking platforms that allow addition/removal of physical interface cards this feature can provide: A) a graceful method to add to the interfaces of an existing association. For the multi-homed IPv6 case this feature will allow renumbering of existing associations. B) provides a method for an endpoint to request that its peer set its primary destination address: This can be useful when an address is about to be deleted. Or when an endpoint has some predetermined knowledge about which is the preferred address to receive SCTP packets upon. - The SCTP flow limit extension: This extension enables the ability to request a sender to set a limit to the outstanding data sent to each stream. This in turn will provide: A) The ability to minimize the occurrence of a single stream monopolizing all transport level resources (e.g. a_rwnd Stewart et.al. [Page 2] Internet Draft Address/Stream Configuration May 2001 "deadlock"). B) The ability to dynamically change the stream buffering limits as the application deems appropriate at any particular instant. 2. Conventions The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in RFC 2119 [RFC2119]. 3. Additional Chunks and Parameters This section describes the addition of two new chunks and, six new parameters to allow: - Dynamic addition of IP Addresses to an association. - Dynamic deletion of IP Addresses to an association. - A request to set the primary address the peer will use when sending to an endpoint. - The setting of stream flow limits. Additionally, this section describes three new error causes that support these new chunks and parameters. 3.1 New Chunk Types This section defines two new Chunk types that will be used to transfer the control information reliably. Table 1 illustrates the two new chunk types. Chunk Type Chunk Name -------------------------------------------------------------- 11000001 Address/Stream Configuration Change Chunk (ASCONF) 10000000 Address Configuration Acknowledgment (ASCONF-ACK) Table 1: Address/Stream Configuration Chunks It should be noted that the ASCONF Chunk format requires the receiver to report to the sender if it does not understand the ASCONF chunk. This is accomplished by setting the upper bits in the Chunk type as described in [RFC2960] section 3.2. Note that the upper two bits in the ASCONF chunk are set to one. As defined in [RFC2960] section 3.2, setting these upper bits in this manner will cause the receiver that does not understand this chunk to skip the chunk and continue processing, but report in an Operation Error Chunk using the 'Unrecognized Chunk Type' cause of error. 3.1.1 Address Configuration Change Chunk (ASCONF) This chunk is used to communicate to the remote endpoint one of the Stewart et.al. [Page 3] Internet Draft Address/Stream Configuration May 2001 configuration change requests that MUST be acknowledged. The information carried in the ASCONF chunk is always in the form of a Tag-Length-Value (TLV) as described in "3.2.1 Optional/Variable-length Parameter Format" in [RFC2960]. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 0xC1 | Chunk Flags | Chunk Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Serial Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ASCONF-Request Correlation ID #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ASCONF Parameter #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ \ / .... / \ \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ASCONF-Request Correlation ID #N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ASCONF Parameter #N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Serial Number : 32 bits (unsigned integer) This value represents a Serial Number for the ASCONF Chunk. The valid range of Serial Number is from 0 to 4294967295 (2**32 - 1). Serial Numbers wrap back to 0 after reaching 4294967295. ASCONF-Request Correlation ID: 32 bits (unsigned integer) This is an opaque integer assigned by the sender to identify each request parameter. It is in host byte order and is only meaningful to the sender. The receiver of the ASCONF chunk will copy this 32 bit value into the ASCONF Correlation ID field of the ASCONF-ACK. The sender of the ASCONF can use this same value in the ASCONF-ACK to find which request the response is for. ASCONF Parameter: TLV format Each Address configuration change is represented by a TLV parameter has defined in Section 3.2. One or more request may be present in a ASCONF chunk. 3.1.2 Address Configuration Acknowledgment Chunk (ASCONF-ACK) This chunk is used by the receiver of an ASCONF chunk to acknowledge its reception. It carries zero or more results for any ASCONF Parameters that were processed by the receiver. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 Stewart et.al. [Page 4] Internet Draft Address/Stream Configuration May 2001 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 0x80 | Chunk Flags | Chunk Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Serial Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ASCONF-Request Correlation ID #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ASCONF Parameter Response#1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ \ / .... / \ \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ASCONF-Request Correlation ID #N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ASCONF Parameter Response#N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Serial Number : 32 bits (unsigned integer) This value represents the Serial Number for the ASCONF chunk that was received to which this Chunk is acknowledgment of. This value is copied from the received ASCONF chunk. ASCONF-Request Correlation ID: 32 bits (unsigned integer) This value is copied from the ASCONF Correlation ID received in the ASCONF chunk. It is used by the receiver of the ASCONF-ACK to identify which ASCONF parameter this response is associated with. ASCONF Parameter Response : TLV format The ASCONF Parameter Response is used in the ASCONF-ACK to report status of ASCONF processing. By default, if a responding endpoint does not include any Error cause a success is indicated. Thus a sender of a ASCONF-ACK MAY indicate complete success of all TLV's in a ASCONF by returning only the Chunk Type, Chunk Flags, Chunk Length (set to 8) and the Serial Number. 3.2 New Parameter Types The six new parameters added follow the format defined in section 3.2.1 of [RFC2960]. Table 2 describes the Parameters. Address Configuration Parameters Parameter Type ------------------------------------------------- Add IP Address 49153 (0xC001) Delete IP Address 49154 (0xC002) Stream Flow limit Request 49155 (0xC003) Error Cause Indication 49156 (0xC004) Set Primary Address 49157 (0xC005) Success report 49158 (0xC006) Table 2: Address Configuration Parameters Stewart et.al. [Page 5] Internet Draft Address/Stream Configuration May 2001 3.2.1 Add IP Address 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 0xC001 | Length = Variable | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address Parameter | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Address Parameter: TLV This field contains an IPv4 or IPv6 address parameter as described in 3.3.2.1 of RFC2960. The complete TLV is wrapped within this parameter. It informs the receiver that the Address specified is to be added to the existing association. An example TLV requesting that the IPv4 address 10.1.1.1 should be made the primary destination address would look as follows: +--------------------------------+ | Type=0xC001 | Length = 12 | +--------------------------------+ | Type=5 | Length = 8 | +----------------+---------------+ | Value=0x0a010101 | +----------------+---------------+ Valid Chunk Appearance The Add IP Address parameter may only appear in the ASCONF chunk type. 3.2.2 Delete IP Address 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type =0xC002 | Length = Variable | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address Parameter | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Address Parameter: TLV This field contains an IPv4 or IPv6 address parameter as described in 3.3.2.1 of [RFC2960]. The complete TLV is wrapped within this parameter. It informs the receiver that the Address specified is to be removed from the existing association. An example TLV deleting the IPv4 address 10.1.1.1 from an existing association would look as follows: Stewart et.al. [Page 6] Internet Draft Address/Stream Configuration May 2001 +--------------------------------+ | Type=0xC002 | Length = 12 | +--------------------------------+ | Type=5 | Length = 8 | +----------------+---------------+ | Value=0x0a010101 | +----------------+---------------+ Valid Chunk Appearance The Delete IP Address parameter may only appear in the ASCONF chunk type. 3.2.3 Stream Flow Limit Change 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type =0xC003 | Length = Variable | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Stream Number 1 | Flow Limit 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ / / \ \ / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Stream Number N | Flow Limit N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Stream Number n : 16 bits (unsigned integer) This is the stream number that is requesting a limit be placed on the sender based on the applications receive buffer sizes. Flow Limit n : 16 bits (unsigned integer) This is the limit the receiver is requesting (in bytes) as to the maximum amount of data that the receiver may accept. Note that the value 0 holds a special meaning described in Section 4.5. Valid Chunk Appearance The Stream Flow Limit Change parameter may only appear in the ASCONF chunk type. 3.2.4 Error Cause Indication 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 0xC004 | Length = Variable | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Stewart et.al. [Page 7] Internet Draft Address/Stream Configuration May 2001 | Error Cause(s) or Return Info on Success | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ When reporting an error this response parameter is used to wrap one or more standard error causes normally found within an SCTP Operational Error or SCTP Abort (as defined in [RFC2960]). The Error Cause(s) follow the format defined in section 3.3.10 of [RFC2960]. Valid Chunk Appearance The Error Cause Indication parameter may only appear in the ASCONF-ACK chunk type. 3.2.5 Set Primary IP Address 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type =0xC005 | Length = Variable | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address Parameter | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Address Parameter: TLV This field contains an IPv4 or IPv6 address parameter as described in 3.3.2.1 of [RFC2960]. The complete TLV is wrapped within this parameter. It requests the receiver to mark the specified address as the primary address to send data to (see section 5.1.2 of [RFC2960]). The receiver MAY mark this as its primary upon receiving this request. An example TLV requesting that the IPv4 address 10.1.1.1 be made the primary destination address would look as follows: +--------------------------------+ | Type=0xC005 | Length = 12 | +--------------------------------+ | Type=5 | Length = 8 | +----------------+---------------+ | Value=0x0a010101 | +----------------+---------------+ Valid Chunk Appearance The Set Primary IP Address parameter may appear in the ASCONF chunk, the INIT, or the INIT-ACK chunk type. The inclusion of this parameter in the INIT or INIT-ACK can be used to indicate an initial preference of primary address. 3.2.6 Success Indication Stewart et.al. [Page 8] Internet Draft Address/Stream Configuration May 2001 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 0xC006 | Length = 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ By default if a responding endpoint does not report an error for any requested TLV, a success is implicitly indicated. Thus a sender of a ASCONF-ACK MAY indicate complete success of all TLV's in a ASCONF by returning only the Chunk Type, Chunk Flags, Chunk Length (set to 8) and the Serial Number. The responding endpoint MAY also choose to explicitly report a success for a requested TLV, by returning a success report ASCONF Parameter Response. Valid Chunk Appearance The Success Indication parameter may only appear in the ASCONF-ACK chunk type. 3.3 New Error Causes Three new Error Causes are added to the SCTP Operational Errors, primarily for use in the ASCONF-ACK chunk. Cause Code Value Cause Code --------- ---------------- 12 Request to delete last remaining IP address. 13 Operation Refused due to resource shortage. 14 Request to delete source IP address. Table 3: New Error Causes 3.3.1 Error Cause: Request to Delete Last remaining IP Address Cause of error --------------- Request to delete last remaining IP address: The receiver of this error sent a request to delete the last IP address from its association with its peer. This error indicates that the request is rejected. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Cause Code=12 | Cause Length=Variable | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ TLV-Copied-From-ASCONF / / \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Stewart et.al. [Page 9] Internet Draft Address/Stream Configuration May 2001 An example of a failed delete in an Error Cause TLV would look as follows in the response ASCONF-ACK message: +--------------------------------+ | Type = 0xC004 | Length = 20 | +--------------------------------+ | Cause=12 | Length = 16 | +----------------+---------------+ | Type= 0xC002 | Length = 12 | +----------------+---------------+ | Type=5 | Length = 8 | +----------------+---------------+ | Value=0x0a010101 | +----------------+---------------+ 3.3.2 Error Cause: Operation Refused due to Resource Shortage Cause of error --------------- This error cause is used to report a failure by the receiver to perform the requested operation due to a lack of resources. The entire TLV that is refused is copied from the ASCONF-REQ into the error cause. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Cause Code=13 | Cause Length=Variable | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ TLV-Copied-From-ASCONF / / \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ An example of a failed addition in an Error Cause TLV would look as follows in the response ASCONF-ACK message: +--------------------------------+ | Type = 0xC004 | Length = 20 | +--------------------------------+ | Cause=13 | Length = 16 | +----------------+---------------+ | Type=0xC001 | Length = 12 | +--------------------------------+ | Type=5 | Length = 8 | +----------------+---------------+ | Value=0x0a010101 | +----------------+---------------+ 3.3.3 Error Cause: Request to Delete Source IP Address Cause of error --------------- Request to delete source IP address: The receiver of this error sent Stewart et.al. [Page 10] Internet Draft Address/Stream Configuration May 2001 a request to delete the source IP address of the ASCONF message. This error indicates that the request is rejected. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Cause Code=14 | Cause Length=Variable | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ TLV-Copied-From-ASCONF / / \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ An example of a failed delete in an Error Cause TLV would look as follows in the response ASCONF-ACK message: +--------------------------------+ | Type = 0xC004 | Length = 20 | +--------------------------------+ | Cause=14 | Length = 16 | +----------------+---------------+ | Type=0xC002 | Length = 12 | +----------------+---------------+ | Type=5 | Length = 8 | +----------------+---------------+ | Value=0x0a010101 | +----------------+---------------+ IMPLEMENTATION NOTE: It is unlikely that an endpoint would source a packet from the address being deleted, unless the endpoint does not do proper source address selection. 4. Procedures This section will lay out the specific procedures for address/stream configuration change chunk type and its processing. 4.1 ASCONF Chunk Procedures When an endpoint has an ASCONF signaled change to be sent to the remote endpoint it should do the following: A1) Create a ASCONF Chunk as defined in section 3.1.1. The chunk should contain all of the TLV('s) of information necessary to be sent to the remote endpoint, and unique correlation identities for each request. A2) A serial number should be assigned to the Chunk. The serial number should be a monotonically increasing number. All serial numbers are defined to be initialized at the start of the association to the same value as the Initial TSN. A3) If no ASCONF chunk is outstanding (un-acknowledged) with the remote peer AND there is less than cwnd bytes of user data Stewart et.al. [Page 11] Internet Draft Address/Stream Configuration May 2001 outstanding send the chunk. A4) Start a T-4 RTO timer, using the RTO value of the selected destination address (normally the primary path see [RFC2960] section 6.4 for details). A5) When the ASCONF-ACK which acknowledges the serial number last sent arrives, stop the T-4 RTO timer and clear the appropriate association and destination error counters as defined in [RFC2960] section 8.1 and 8.2. A6) Process all of the TLV's within the ASCONF-ACK to find out particular status information returned to the various requests that were sent. Use the Correlation IDs to correlate the request and the responses. A7) If an error response is received to a TLV whose parameter type all TLVs with no response before the failed TLV are considered successful if not reported. All TLVs after the failed response are considered unsuccessful unless a specific success indication is present for the parameter. A8) If there are no responses to TLVs whose parameter type begins all TLVs not responded to are considered successful. If the T-4 RTO timer expires the endpoint should do the following: B1) Increment the error counter and perform path failure detection on the appropriate destination address as defined in [RFC2960] section 8.2. B2) Increment the association error counter and perform endpoint failure detection on the association as defined in [RFC2960] section 8.1. B3) Back-off the destination address RTO timer to which the ASCONF chunk was sent. B4) Re-transmit the ASCONF chunk last sent and if possible choose an alternate destination address (please refer to [RFC2960] section 6.4.1). An endpoint MUST NOT add new parameters to this chunk, it MUST be the same (including its serial number) as the last ASCONF sent. B5) Restart the T-4 RTO timer. Note if a different destination is selected, then the RTO used will be that of the new destination address. Note: That the the total number of re-transmissions is limited by B2 above. If the maximum is reached the association will fail and enter a CLOSED state (see [RFC2960] section 6.4.1 for details). 4.1.1 Congestion Control of ASCONF Chunks Stewart et.al. [Page 12] Internet Draft Address/Stream Configuration May 2001 In defining the ASCONF chunk transfer procedures it is essential that these transfers MUST NOT cause congestion within the network. To achieve this we place these restrictions on the transfer of ASCONF chunks: R1) One and only one ASCONF Chunk MAY be in transit and unacknowledged at any one time. If a sender, after sending a ASCONF chunk, decides it needs to transfer another ASCONF Chunk, it MUST wait until the ASCONF-ACK Chunk returns from the previous ASCONF Chunk before sending a subsequent ASCONF. Note this restriction binds each side, so at any time two ASCONF may be in-transit on any given association (one sent from each endpoint). R2) A ASCONF MUST NOT be sent if there is no room in the current cwnd. If there is room in the cwnd of the destination network the Chunk may be sent regardless of the value of rwnd. R3) A ASCONF may be bundled with any other Chunk type except other ASCONF chunks. R4) A ASCONF-ACK may be bundled with any other Chunk type except other ASCONF-ACK's. R5) Both ASCONF and ASCONF-ACK chunks MUST NOT be sent in any SCTP state except ESTABLISHED. R6) An ASCONF and respective ASCONF-ACK MUST NOT be larger than the path MTU of the destination. If the sender of a ASCONF chunk receives a Operational Error indicating that the ASCONF chunk type is not understood, then the sender MUST not send subsequent ASCONF chunks to the peer. The endpoint should also inform the upper level application that the peer endpoint does not support any of the extensions detailed in this document. 4.2 Upon reception of a ASCONF Chunk. When an endpoint receives a ASCONF chunk from the remote peer it should perform the following: C1) Compare the value of the serial number to the value the endpoint stored in a new association variable 'Peer-Serial-Number'. This value MUST be initialized to the Initial TSN value minus 1. C2) If the value found in the serial number is equal to the the ('Peer-Serial-Number' + 1), the endpoint should: V1) Process the TLV's contained within the Chunk performing the appropriate actions as indicated by each TLV type. The TLV's MUST be processed in order within the Chunk. In other words if the sender puts 3 TLV's in one chunk the first TLV (the one closest to the Chunk Header) in the Chunk MUST be processed first. The next TLV in Stewart et.al. [Page 13] Internet Draft Address/Stream Configuration May 2001 the chunk (the middle one) would be processed second and finally the last TLV in the Chunk would be processed last. V2) In processing the chunk, the receiver should build a response message with the appropriate error TLV's, as specified in the Parameter type bits for any ASCONF Parameter it does not understand. To indicate an unrecognized parameter, parameter type 8 as defined in in the INIT-ACK in 3.3.3 of [RFC2960] should be used. It may also use the response to carry rejections for other reasons such as resource shortages etc using the Error Cause TLV and an appropriate error condition. Note: a positive response is implied if no error is indicated by the sender. V3) All error responses must copy the ASCONF-Request Correlation ID field received in the ASCONF, from the TLV being responded to, into the ASCONF-Request Correlation ID field. The ASCONF-Request Correlation ID always precedes the request TLV. V4) After processing the entire Chunk, it MUST send all TLV's for both unrecognized parameters and any other status TLV's inside the ASCONF-ACK chunk that acknowledges the arrival and processing of the ASCONF Chunk. V5) Update the 'Peer-Serial-Number' to the value found in the serial number field. C3) If the value found in the serial number is equal to the value stored in the 'Peer-Serial-Number', the endpoint should: X1) Parse the ASCONF Chunk TLV's but the endpoint MUST not take any action on the TLV's parsed (since it has already performed these actions). X2) Build a response message with the appropriate response TLV's as specified in the ASCONF Parameter type bits, for any parameter it does not understand or could not process. X3) After parsing the entire Chunk, it MUST send any response TLV errors and status with a ASCONF-ACK chunk acknowledging the arrival and processing of the ASCONF Chunk. X4) The endpoint MUST NOT update its 'Peer-Serial-Number'. IMPLEMENTATION NOTE: As an optimization a receiver may wish to save the last ASCONF-ACK for some predetermined period of time and instead of re-processing the ASCONF (with the same serial number) it may just re-transmit the ASCONF-ACK. It may wish to use the arrival of a new serial number to discard the previously saved ASCONF-ACK or any other means it may choose to expire the saved ASCONF-ACK. C4) Otherwise, the ASCONF chunk is discarded since it must be either a stale packet or from an attacker. A receiver of such a packet MAY Stewart et.al. [Page 14] Internet Draft Address/Stream Configuration May 2001 log the event for security purposes. C5) In both cases C2 and C3 the ASCONF-ACK MUST be sent back to the source address contained in the IP header of the ASCONF being responded to. 4.3 General rules for address manipulation When building TLV parameters for the ASCONF Chunk that will add or delete IP addresses the following rules should be applied: D1) When adding an IP address to an association, the IP address is NOT considered fully added to the association until the ASCONF-ACK arrives. This means that until such time as the ASCONF containing the add is acknowledged the sender MUST NOT use the new IP address as a source for ANY SCTP packet. The receiver of the add IP address request may use the address has a destination immediately. D2) After the ASCONF-ACK of an IP address add arrives, the endpoint MAY begin using the added IP address as a source address. D3) If an endpoint receives an Error Cause TLV indicating that the IP address Add, IP address Deletion, or Set Primary IP Address parameters was not understood, the endpoint MUST consider the operation failed and MUST NOT attempt to send any subsequent Add, Delete or Set Primary requests to the peer. D4) When deleting an IP address from an association, the IP address MUST be considered a valid destination address for the reception of SCTP packets until the ASCONF-ACK arrives and MUST NOT be used has a source address for any subsequent packets. This means that any datagrams that arrive before the ASCONF-ACK destined to the IP address being deleted MUST be considered part of the current association. One special consideration is that ABORT chunks arriving destined to the IP address being deleted MUST be ignored (see Section 4.3.1 for further details). D5) An endpoint MUST NOT delete its last remaining IP address from an association. In other words if an endpoint is NOT multi-homed it MUST NOT use the delete IP address. Or if an endpoint sends multiple requests to delete IP addresses it MUST NOT delete all of the IP addresses that the peer has listed for the requester. D6) An endpoint MUST NOT set a source address for an SCTP packet holding the ASCONF chunk to be the same as an address being deleted by the ASCONF chunk. D7) If a request is received to delete the last remaining IP address of a peer endpoint, the receiver MUST send an Error Cause TLV with the error cause set to the new error code 'Request to delete last IP remaingin address'. The requested delete MUST NOT be performed or acted upon, other than to send the ASCONF-ACK. Stewart et.al. [Page 15] Internet Draft Address/Stream Configuration May 2001 D8) If a request is received to delete an IP address which is also the source address of the IP packet which contained the ASCONF chunk, the receiver MUST reject this request. To reject the request the receiver MUST send an Error Cause TLV set to the new error code "Request to Delete Source IP Address" (unless Rule D5 has also been violated, in which case the error code 'Request to delete last remaining IP address' is sent). D9) If an endpoint receives an ADD IP address request and does not have the local resources to add this new address to the association, it MUST return an Error Cause TLV set to the new error code "Operation Refused due to Resource Shortage". D10) If an endpoint receives an 'Out of Resource' error in response to its request to ADD an IP address to an association, it must either ABORT the association or not consider the address part of the association. In other words if the endpoint does not ABORT the association, it must consider the add attempt failed and NOT use this address and treat SCTP packets destined to the address as Out Of The Blue packets. D11) When an endpoint receiving a ASCONF to add an IP address sends an 'Out of Resource' in its response, it MUST also fail any subsequent add or delete requests bundled in the ASCONF. The receiver MUST NOT reject an ADD and then accept a subsequent DELETE of an IP address in the same ASCONF chunk. In other words, once a receiver begins failing any ADD or DELETE request, it must fail all subsequent ADD or DELETE requests contained in that single ASCONF. D12) When an endpoint receives a request to delete an IP address that is the current primary address, it is an implementation decision as to how that endpoint chooses the new primary address. D13) When an endpoint receives a valid request to DELETE an IP address the endpoint MUST consider the address no longer as part of the association. It MUST NOT send SCTP packets for the association to that address and it MUST treat subsequent packets received from that address as Out Of The Blue. During the time interval between sending out the ASCONF and receiving the ASCONF-ACK it MAY be possible to receive DATA chunks out of order. The following examples illustrate these problems: Endpoint-A Endpoint-Z ---------- ---------- ASCONF[Add-IP:X]------------------------------> /--ASCONF-ACK / /--------/---New DATA: / / Destination <-------------------/ / IP:X / <--------------------------/ Stewart et.al. [Page 16] Internet Draft Address/Stream Configuration May 2001 In the above example we see a new IP address (X) being added to the Endpoint-A. However due to packet re-ordering in the network a new DATA chunk is sent and arrives at Endpoint-A before the ASCONF-ACK confirming the add of the address to the association. A similar problem exists with the deletion of an IP address as follows: Endpoint-A Endpoint-Z ---------- ---------- /------------New DATA: / Destination / IP:X ASCONF [DEL-IP:X]---------/----------------> <-----------------/------------------ASCONF-ACK / / <-------------/ In this example we see a DATA chunk destined to the IP:X (which is about to be deleted) arriving after the deletion is complete. For the ADD case an endpoint SHOULD consider the newly adding IP address valid for the association to receive data from during the interval when awaiting the ASCONF-ACK. The endpoint MUST NOT source data from this new address until the ASCONF-ACK arrives but it may receive out of order data as illustrated and MUST NOT treat this data as an OOTB datagram (please see [RFC2960] section 8.4). It MAY drop the data silently or it MAY consider it part of the association but it MUST NOT respond with an ABORT. For the DELETE case, an endpoint MAY respond to the late arriving DATA packet as an OOTB datagram or it MAY hold the deleting IP address for a small period of time as still valid. If it treats the DATA packet as an OOTB the peer will silently discard the ABORT (since by the time the ABORT is sent the peer will have removed the IP address from this association). If the endpoint elects to hold the IP address valid for a period of time, it MUST NOT hold it valid longer than 2 RTO intervals for the destination being removed. 4.3.1 A special case for OOTB ABORT chunks Another case worth mentioning is illustrated below: Endpoint-A Endpoint-Z ---------- ---------- New DATA:------------\ Source IP:X \ \ ASCONF-REQ[DEL-IP:X]----\------------------> \ /---------ASCONF-ACK \ / \----/-----------> OOTB Stewart et.al. [Page 17] Internet Draft Address/Stream Configuration May 2001 (Ignored <---------------------/-------------ABORT by rule D4) / <---------------------/ For this case, during the deletion of an IP address, an Abort MUST be ignored if the destination address of the Abort message is that of the destination being deleted. 4.4 Setting of the primary address A sender of this option may elect to send this combined with a deletion or addition of an address. A sender SHOULD only send a set primary request to an address that is already considered part of the association. In other words if a sender combines a set primary with an add of a new IP address the set primary will be discarded unless the add request is to be processed BEFORE the set primary (i.e. it preceeds the set primary). A request to set primary MAY also appear in a INIT or INIT-ACK chunk. This can give a hint to the peer endpoint as to which of its addresses the sender of the INIT or INIT-ACK would like to be used as the primary address. The request to set an address as the primary path is an option the receiver MAY perform. It is considered a hint to the receiver of the best destination address to use in sending SCTP packets (in the requester's view). It is possible that the receiver may have other knowledge that it may act upon and NOT set the specified address as primary. If a request arrives that asks the receiver to set an address as primary that does not exist, the receiver should NOT honor the request, leaving its existing primary address unchanged. 4.5 Steam Flow Limit Procedures A stream in SCTP is an uni-directional logical channel established from one to another associated SCTP endpoint, within which all user messages are delivered in sequence except for those submitted to the un-ordered delivery service which may arrive out of sequence. Since each stream is uni-directional and no feedback mechanism exists to limit a sender, it is possible for one unique stream to monopolize all of the transport level receiver window space. The mechanism defined here attempts to alleviate this problem by allowing the receiver side to communicate to the sender a limit on how much outstanding data may be sent within a particular stream. The procedures defined here are broken down into two sides: o The stream receiver side or peer requesting the limit. And, o the stream sender side or peer that MUST honor the limit request. The receivers side is mainly involved with sending the request to the peer. The senders side is where the actual limitations and flow limit will occur. Note in section 4.5.1 the stream receiver is the Stewart et.al. [Page 18] Internet Draft Address/Stream Configuration May 2001 endpoint that sends the ASCONF message, in section 4.5.2 the sender side is the endpoint that receives the ASCONF message. 4.5.1 Stream Receiver side procedures The receiver side SCTP makes decisions on stream flow limit based on upper layer input. Normally the upper layer makes a request to limit all or a subset of the active streams that send data to it via an API interface. How this decision is made is outside the scope of this document. Anytime flow limits are made known to the SCTP endpoint by the application, the receiver side SHOULD create a ASCONF Chunk and attach to it one or more stream flow limits with there respective stream number. If the receiver wishes to remove all limits (previously placed on a particular stream) it may do so by placing the special value '0' in the 'Flow Limit' field. Once acknowledged by the peer endpoint the receiver should consider the limit in place. Note that the parameter type field upper two bits dictates that any parameter not understood should be skipped and reported to the sender with an Operational Error. If an Operational Error is received that indicates that the 'Stream Flow Limit Request' is not understood, the sender of the limit request MUST not send subsequent limit requests. The endpoint SHOULD also inform the upper level application that the peer endpoint does not support this feature. 4.5.2 Stream Sender side procedures When a 'Stream Flow Limit Request' is received the sender MUST record each flow limit with its appropriate stream. After a limit is set on a stream the sender MUST obey the following rules when sending to the peer on that stream: S1) When the upper layer application attempts to send to the peer on a stream, check the number of outstanding bytes sent to that stream (those TSN's in queue to be sent, which the cumulative TSN Acknowledgment has not passed, on this stream) versus the limit set for that stream (The last received limit for this stream is henceforth termed the current limit). S2) If the number of outstanding bytes is greater than or equal to the current limit, the SCTP endpoint MUST reject the request and NOT queue the data for transmit. Instead it SHOULD return an error to the sending application. S3) If the number of outstanding bytes is less than the current limit, validate that the data to be sent plus the number of outstanding bytes is smaller than or equal to this limit. If the user data plus the number of outstanding bytes is smaller than or equal to the current limit accept the data for transmit and queue the user data (increasing the number of outstanding data bytes on Stewart et.al. [Page 19] Internet Draft Address/Stream Configuration May 2001 this stream). If the user data plus the number of outstanding bytes is larger than the current limit for this stream, the SCTP endpoint MUST reject the request and NOT queue the data for transmit and instead SHOULD return an error to the application. S4) Any time a stream limit is updated to the value of 0, consider this indication to mean no limit is in effect for this stream. 4.5.3 ULP considerations on the use of SCTP flow limit facility The effect of rule S3 in section 4.5.2 places a maximum size upon a sender. Once a limit is in effect, if the sending Upper Layer Protocol (ULP) wishes to send a message that is larger than that permitted by the imposed stream limit, the ULP will need to provide a mechanism for fragmentation and re-assembly. This ULP mechanism is in addition to any fragmentation and re-assembly that may be provided by SCTP. It is the sole responsibility of the ULP to handle the case of a single user message being larger than the stream flow limit, if applicable. 5. Security Considerations The ADD/DELETE of an IP address to an existing association does provide an additional mechanism by which existing associations can be hijacked. Where the attacker is able to intercept and or alter the packets sent and received in an association the use of this feature MAY increase the ease at which an association may be overtaken. This threat SHOULD be considered when deploying a version of SCTP that use this feature. The IP Authentication Header [RFC2402] SHOULD be used when the threat environment requires stronger integrity protections, but does not require confidentiality. It should be noted that in the base SCTP specification [RFC2960], if an attacker is able to intercept and or alter packets, even without this feature it is possible to hijack an existing association, please refer to Section 11 of RFC2960. 6. IANA considerations This document defines the following new SCTP parameters, chunks and errors: - Two new Chunk Types, - Six Parameter Types, and - Three new SCTP Error Causes. 7. Acknowledgements The authors wish to thank Jon Berger, John Loughney, Ivan Rodriguez, Marshall Rose, and Chip Sharp for their invaluable comments. 8. Authors' Addresses Stewart et.al. [Page 20] Internet Draft Address/Stream Configuration May 2001 Randall R. Stewart Tel: +1-815-477-2127 Cisco Systems, Inc. EMail: rrs@cisco.com 8745 W. Higgins Road, Suite 200 Chicago, Ill 60631 USA Micheal A. Ramalho Tel: +1-732-809-0188 Cisco Systems, Inc. EMail: mramalho@cisco.com 1802 Rue de la Porte Wall Township, NJ 0719-3784 Qiaobing Xie Tel: +1-847-632-3028 Motorola, Inc. EMail: qxie1@email.mot.com 1501 W. Shure Drive, #2309 Arlington Heights, IL 60004 USA Michael Tuexen Tel: +49-89-722-47210 SIEMENS AG EMail: Michael.Tuexen@icn.siemens.de Hofmannstr. 51 81359 Munich Germany Ian Rytina Tel: +61-3-9301-6164 Ericsson Australia EMail:ian.rytina@ericsson.com 37/360 Elizabeth Street Melbourne, Victoria 3000 Australia Phil Conrad Tel: +1-XXX-XXX-XXXX Netlab Research Group Email conrad@joda.cis.temple.edu Dept. Of Computer & Information Sciences Temple University 1805 N Broad St. Philadelphia, PA 19122 USA 9. References [RFC2960] R. R. Stewart, Q. Xie, K. Morneault, C. Sharp, H. J. Schwarzbauer, T. Taylor, I. Rytina, M. Kalla, L. Zhang, and, V. Paxson, "Stream Control Transmission Protocol," RFC 2960, October 2000. [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 3", RFC 2026, October 1996. [RFC2119] Bradner, S. "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2402] S. Kent, R. Atkinson., "IP Authentication Header.", RFC 2402, November 1998. Stewart et.al. [Page 21] Internet Draft Address/Stream Configuration May 2001 This Internet Draft expires in 6 months from May, 2001 Stewart et.al. [Page 22]