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 Novmeber 19, 2001 SCTP Extensions for Dynamic Reconfiguration 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 methods to (1) reconfigure IP address information on an existing association and (2) request that a peer set flow limits in units of bytes or messages, either on a per-stream or per-association basis. TABLE OF CONTENTS 1. Introduction............................................... 2 2. Conventions................................................ 2 3. Additional Chunks and Parameters........................... 3 3.1 New Chunk Types........................................... 3 3.1.1 Address/Stream Configuration Change Chunk (ASCONF)...... 3 3.1.2 Address/Stream Configuration Acknowledgment Chunk (ASCONF-ACK)............................................ 5 3.2 New Parameter Types....................................... 6 3.2.1 Add IP Address.......................................... 6 Stewart et.al. [Page 1] Internet Draft Dynamic address reconfiguration November 2001 3.2.2 Delete IP Address....................................... 7 3.2.3 Error Cause Indication.................................. 7 3.2.4 Set Primary IP Address.................................. 8 3.2.5 Success Indication...................................... 8 3.2.6 Adaption Layer Indication............................... 9 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........11 4. Procedures.................................................11 4.1 ASCONF Chunk Procedures...................................11 4.1.1 Congestion Control of ASCONF Chunks.....................13 4.2 Upon reception of an ASCONF Chunk.........................14 4.3 General rules for address manipulation....................15 4.3.1 A special case for OOTB ABORT chunks....................18 4.3.2 A special case for changing an address..................19 4.4 Setting of the primary address............................19 5. Security Considerations....................................19 6. IANA considerations........................................20 7. Authors' Addresses.........................................20 8. References.................................................21 1. Introduction To extend the utility and application scenarios of SCTP, this document introduces optional extensions that provide SCTP with the ability to reconfigure IP address information on an existing association. This extension enable SCTP to be utilized in the following applications: - Dynamic IP address reconfiguration 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 IPv6 this feature allows renumbering of existing associations. B) 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. 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]. Stewart et.al. [Page 2] Internet Draft Dynamic address reconfiguration November 2001 3. Additional Chunks and Parameters This section describes the addition of two new chunks and, eight 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. 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 -------------------------------------------------------------- 0xC1 Address/Stream Configuration Change Chunk (ASCONF) 0x80 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/Stream Configuration Change Chunk (ASCONF) This chunk is used to communicate to the remote endpoint one of the configuration change requests that MUST be acknowledged. The information carried in the ASCONF Chunk uses the form of a Tag-Length-Value (TLV), as described in "3.2.1 Optional/Variable-length Parameter Format" in [RFC2960], for all variable parameters. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Addr Type | Stewart et.al. [Page 3] Internet Draft Dynamic address reconfiguration November 2001 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address Bytes 0-3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address Bytes 4-7 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address Bytes 8-11 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address Bytes 12-15 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 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. Reserved: 24 bits Reserved, set to 0 by the sender and ignored by the receiver. Address Type : 8 bits (unsigned char) This value determines the type of address found in the Address Bytes field. If the value is 5 then the first 4 bytes of the Address Bytes field contain an IPv4 address, in network byte order. If the value is 6 then the first 16 bytes of the Address Bytes field contain an IPv6 address, in network byte order. Address Bytes: 16 bytes (unsigned chars) This field contains an IP address of the sender of the ASCONF chunk, the address MUST be considered part of the association by the peer endpoint (the receiver of the ASCONF chunk). This field may be used by the receiver of the ASCONF to help in finding the association. 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 Stewart et.al. [Page 4] Internet Draft Dynamic address reconfiguration November 2001 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 as defined in Section 3.2. One or more requests may be present in an ASCONF Chunk. 3.1.2 Address/Stream Configuration Acknowledgment Chunk (ASCONF-ACK) This chunk is used by the receiver of an ASCONF Chunk to acknowledge the 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 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 received ASCONF Chunk that is acknowledged by this chunk. 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 Stewart et.al. [Page 5] Internet Draft Dynamic address reconfiguration November 2001 sender of an ASCONF-ACK MAY indicate complete success of all TLVs in an ASCONF by returning only the Chunk Type, Chunk Flags, Chunk Length (set to 8) and the Serial Number. 3.2 New Parameter Types The eight 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 0xC001 Delete IP Address 0xC002 Error Cause Indication 0xC004 Set Primary Address 0xC005 Success report 0xC006 Table 2: Address Configuration Parameters 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 be added to the association 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. Stewart et.al. [Page 6] Internet Draft Dynamic address reconfiguration November 2001 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: +--------------------------------+ | 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 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 = 0xC003 | Length = Variable | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 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. Stewart et.al. [Page 7] Internet Draft Dynamic address reconfiguration November 2001 3.2.4 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 =0xC004 | 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=0xC004 | 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. 3.2.5 Success 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 = 0xC005 | 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 TLVs in an 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 an Stewart et.al. [Page 8] Internet Draft Dynamic address reconfiguration November 2001 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. 3.2.6 Adaption Layer 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 =0xC006 | Length = Variable | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved Bit Fields | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ This parameter is specified for the communication of peer upper layer protocols. It is envisioned to be used for flow control and other adaption layers that require an indication to be carried in the INITand INIT-ACK. Each adaption layer that is defined that wishes to use this parameter MUST specify a bit int the reserved bit field in an appropriate RFC. This parameter SHOULD NOT be examined by the receiving SCTP implementation and should be passed opaquely to the upper layer protocol. Valid Chunk Appearance The Adaption Layer Indication parameter may appear in INIT or INIT-ACK chunk and SHOULD be passed to the receivers upper layer protocol. 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 --------- ---------------- 0xC Request to Delete Last Remaining IP Address. 0xD Operation Refused Due to Resource Shortage. 0xE 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 Stewart et.al. [Page 9] Internet Draft Dynamic address reconfiguration November 2001 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=0x000C | 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=0x000C | Length = 16 | +----------------+---------------+ | Type= 0xC002 | Length = 12 | +----------------+---------------+ | Type=0x0005 | 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=0x000D | 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=0x000D | Length = 16 | +----------------+---------------+ Stewart et.al. [Page 10] Internet Draft Dynamic address reconfiguration November 2001 | Type=0xC001 | Length = 12 | +--------------------------------+ | Type=0x0005 | 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 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=0x000E | 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=0x000E | Length = 16 | +----------------+---------------+ | Type=0xC002 | Length = 12 | +----------------+---------------+ | Type=0x0005 | 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: Stewart et.al. [Page 11] Internet Draft Dynamic address reconfiguration November 2001 A1) Create an 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 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 that 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 TLVs 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 for a TLV parameter, 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 is no response(s) to specific TLV parameter(s), and no failures are indicated, then all request(s) are considered successful. If the T-4 RTO timer expires the endpoint should do the following: B1) Increment the error counters and perform path failure detection on the appropriate destination address as defined in [RFC2960] section 8.1 and 8.2. B2) Increment the association error counters and perform endpoint failure detection on the association as defined in [RFC2960] section 8.1 and 8.2. B3) Back-off the destination address RTO value to which the ASCONF chunk was sent by doubling the RTO timer value. Note: The RTO value is used in the setting of all timer types for SCTP. Each destination address a single RTO estimate. Stewart et.al. [Page 12] Internet Draft Dynamic address reconfiguration November 2001 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 that if a different destination is selected, then the RTO used will be that of the new destination address. Note: 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 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 an 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-ACKs. R5) Both ASCONF and ASCONF-ACK chunks MUST NOT be sent in any SCTP state except ESTABLISHED. R6) An ASCONF MUST NOT be larger than the path MTU of the destination. R7) An ASCONF-ACK SHOULD not be larger than the path MTU. In some circumstances a ASCONF-ACK may exceed the path MTU and in such a case IP fragmentation must be used. If the sender of an 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 layer application that the peer endpoint does not support any of the extensions detailed in this document. Stewart et.al. [Page 13] Internet Draft Dynamic address reconfiguration November 2001 4.2 Upon reception of an ASCONF Chunk. When an endpoint receives an ASCONF Chunk from the remote peer special procedures MAY be needed to identify the association the ASCONF Chunk is associated with. To properly find the association the following procedures should be followed: L1) Use the source address and port number of the sender to attempt to identify the association (i.e. use the same method defined in [RFC2960] used for all other SCTP chunks ). If found proceed to rule L4. L2) If the association is not found, use the address found in the Address Bytes field combined with the port number found in the SCTP common header. If found proceed to rule L4. L3) If neither L1 or L2 locates the association, treat the chunk as an Out Of The Blue chunk as defined in [RFC2960]. L4) Follow the normal rules to validate the SCTP verification tag found in [RFC2960]. After identification and verification of the association, the following should be performed to properly process the ASCONF Chunk: 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 ('Peer-Serial-Number' + 1), the endpoint MUST: V1) Process the TLVs contained within the Chunk performing the appropriate actions as indicated by each TLV type. The TLVs MUST be processed in order within the Chunk. For example, if the sender puts 3 TLVs in one chunk, the first TLV (the one closest to the Chunk Header) in the Chunk MUST be processed first. The next TLV in the chunk (the middle one) MUST be processed second and finally the last TLV in the Chunk MUST be processed last. V2) In processing the chunk, the receiver should build a response message with the appropriate error TLVs, as specified in the Parameter type bits for any ASCONF Parameter it does not understand. To indicate an unrecognized parameter, cause type 8 as defined in in the INIT-ACK in 3.3.10.8 of [RFC2960] should be used. The endpoint 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 Stewart et.al. [Page 14] Internet Draft Dynamic address reconfiguration November 2001 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 TLVs for both unrecognized parameters and any other status TLVs 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 TLVs but the endpoint MUST NOT take any action on the TLVs parsed (since it has already performed these actions). X2) Build a response message with the appropriate response TLVs 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 an 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 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: Stewart et.al. [Page 15] Internet Draft Dynamic address reconfiguration November 2001 D0) If an endpoint receives an ASCONF-ACK but no ASCONF chunk is outstanding AND the sequence number of the ASCONF-ACK matches what WOULD be the next sequence number sent by the endpoint the endpoint MUST abort the association. 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 except on carrying an ASCONF chunk. The receiver of the add IP address request may use the address as 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 for any type of SCTP chunk. D3a) If an endpoint receives an Error Cause TLV indicating that the IP address Add or IP address Deletion parameters was not understood, the endpoint MUST consider the operation failed and MUST NOT attempt to send any subsequent Add or Delete requests to the peer. D3b) If an endpoint receives an Error Cause TLV indicating that the IP address Set Primary IP Address parameter was not understood, the endpoint MUST consider the operation failed and MUST NOT attempt to send any subsequent Set Primary IP Address 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 as 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 without an add IP address preceding the delete parameter in the ASCONF chunk. 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 IP header 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 Remaining IP Address'. The requested delete MUST NOT be performed or acted upon, other than to send the ASCONF-ACK. Stewart et.al. [Page 16] Internet Draft Dynamic address reconfiguration November 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 since its peer will treat SCTP packets destined to the address as Out Of The Blue packets. D11) When an endpoint receiving an 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 17] Internet Draft Dynamic address reconfiguration November 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 (Ignored <---------------------/-------------ABORT Stewart et.al. [Page 18] Internet Draft Dynamic address reconfiguration November 2001 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 a destination being deleted. 4.3.2 A special case for changing an address. In some instances the sender may only have one IP address in an association that is being renumbered. When this occurs, the sender may not be able to send to the peer the appropriate ADD/DELETE pair and use the old address as a source in the IP header. For this reason the sender MUST fill in the Address Bytes field with an address that is part of the association (in this case the one being deleted). This will allow the receiver to locate the association without using the source address found in the IP header. The receiver of such a chunk MUST always first use the source address found in the IP header in looking up the association. The receiver should attempt to use the address found in the Address Bytes field only if the lookup fails using the source address from the IP header. The receiver MUST reply to the source address of the packet in this case which is the new address that was added by the ASCONF (since the old address is no longer a part of the association after processing). 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 precedes the set primary). A request to set primary MAY also appear in a INIT or INIT-ACK chunk. This can give advice to the peer endpoint as to which of its addresses the sender of the INIT or INIT-ACK would prefer to be used as the primary address. The request to set an address as the primary path is an option the receiver SHOULD perform. It is considered advice to the receiver of the best destination address to use in sending SCTP packets (in the requester's view). 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. 5. Security Considerations The ADD/DELETE of an IP address to an existing association does Stewart et.al. [Page 19] Internet Draft Dynamic address reconfiguration November 2001 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 with which an association may be overtaken. This threat SHOULD be considered when deploying a version of SCTP that makes use of 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. Acknowledgments The authors wish to thank Maria-Carmen Belinchon, Jon Berger, Peter Lei, John Loughney, Ivan Arias Rodriguez, Renee Revis, Marshall Rose, and Chip Sharp for their invaluable comments. 8. Authors' Addresses 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 Stewart et.al. [Page 20] Internet Draft Dynamic address reconfiguration November 2001 Ericsson Australia EMail:ian.rytina@ericsson.com 37/360 Elizabeth Street Melbourne, Victoria 3000 Australia Phil Conrad Tel: +1-215-204-7910 Netlab Research Group Email conrad@acm.org 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. This Internet Draft expires in 6 months from May, 2001 Stewart et.al. [Page 21]