INIT Forwarding for the Stream Control Transmission Protocol

Abstract

The Stream Control Transmission Protocol (SCTP) extension described in this document allows the support of a simple mechanism to distribute association requests between a cluster of SCTP end points providing the same service. In particular, this allows the use of anycast addresses in combination with SCTP.¶

1. Introduction

The protocol extension described in this document allows an initiation of an SCTP association to deal with an address change of the peer during the handshake. The extension enables the peer to respond from another address than the one used as destination address in the received packet containing the INIT chunk. The SCTP Dynamic Address Reconfiguration extension described in [RFC5061] can not be used, since it does not apply to the handshake.¶

3. A New Chunk Parameter

The INIT Forwarding Chunk Parameter is defined by the following figure.¶

 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 = 0x8006         |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\                                                               \
/                           Parameter                           /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type: 16 bits (unsigned integer)

This field holds the IANA defined parameter type for the "INIT Forwarding" chunk parameter. IANA is requested to assign the value 32774 (0x8006) for this parameter type.¶

Length: 16 bits (unsigned integer)

This field holds the length in bytes of the chunk parameter; the value MUST be the length of the parameter included plus 4.¶

Parameter: variable length

The parameter MUST be one of:¶

• IPv4 Address parameter as specified in [RFC9260].¶

• IPv6 Address parameter as specified in [RFC9260].¶

• Padding parameter as specified in [RFC4820]. The length of the Padding parameter MUST be either the length of an IPv4 Address parameter or the length of the IPv6 Address parameter.¶

All transported integer numbers are in "network byte order" a.k.a., Big Endian.¶

The INIT Forwarding Chunk Parameter MAY appear in INIT and INIT ACK chunks and MUST NOT appear in any other chunk. If an INIT or INIT ACK chunk contains an INIT Forwarding Chunk Parameter, the INIT Forwarding Chunk Parameter MUST be the first optional/variable-length parameter.¶

If an end point not supporting the extension described in this document receives this parameter in an INIT or INIT ACK chunk, it skips this parameter and continues to process further parameters in the chunk. This behaviour is REQUIRED by [RFC9260] because the highest-order 2 bits of the Type are 10.¶

4. Procedures

If an end point that sends an SCTP packet containing an INIT chunk wants to allow the peer to respond from an address different from the destination address of the packet, MUST use the INIT Forwarding Chunk parameter as the first optional/variable-length parameter. The parameter in the INIT Forwarding Chunk parameter MUST be a Padding parameter. If the SCTP packet containing the INIT chunk is sent over IPV4, the length of the padding parameter MUST be the length of an IPv4 Address parameter, which is 8 bytes. Otherwise, if the SCTP packet containing the INIT chunk is sent over IPV6, the length of the padding parameter MUST be the length of an IPv6 Address parameter, which is 20 bytes.¶

If a middlebox receives an SCTP packet containing an INIT chunk with INIT Forwarding Chunk parameter as its first optional/variable-length parameter and wants to change the destination address of the packet, it MUST replace the Padding parameter in the INIT Forwarding Chunk parameter with an IPv4 or IPv6 Address parameter containing the original destination address of the SCTP packet containing the INIT chunk. If the INIT Forwarding Chunk parameter does not contain a Padding parameter, but an IPv4 or IPv6 Address parameter, the INIT Forwarding Chunk parameter MUST NOT be modified at all.¶

If an end point receives an SCTP packet containing an INIT chunk and the INIT chunk contains an INIT Forwarding Chunk parameter including an Address parameter as its first optional/variable-length parameter, the end point MUST include this INIT Forwarding Chunk parameter as the first optional/variable-length parameter in the INIT ACK chunk, which is sent in response. If the INIT Forwarding Chunk parameter contains a Padding parameter and the end-point does not want to use the destination address, it MUST put an INIT Forwarding Chunk parameter containing this address in the INIT ACK chunk sent in response. If the end point wants to use the destination address in the association and the INIT Forwarding Chunk parameter contains a Padding parameter, the INIT Forwarding Chunk parameter MUST NOT be included in the INIT ACK chunk.¶

If an end point receives an SCTP packet containing an INIT ACK chunk and it cannot find the association for this packet using the IP addresses and port numbers, and the INIT ACK chunk contains an INIT Forwarding Chunk parameter as its first optional/variable-length parameter, it SHOULD use the IP address contained in the Address parameter of the INIT Forwarding Chunk parameter instead of the source address of the received packet for the association lookup. If an association is then found, the address in the INIT Forwarding Chunk parameter MUST be removed as a remote address and the source address of the packet containing the INIT ACK chunk MUST be added as an unconfirmed remote address.¶

5. Socket API Considerations

This section describes how the socket API defined in [RFC6458] needs to be extended to provide a way for the application to control the UDP encapsulation.¶

Please note that this section is informational only.¶

A socket API implementation based on [RFC6458] is extended by supporting one new read/write IPPROTO_SCTP level socket option.¶

6. IANA Considerations

[NOTE to RFC-Editor: "RFCXXXX" is to be replaced by the RFC number you assign this document.]¶

[NOTE to RFC-Editor: The requested value for the parameter type is tentative and to be confirmed by IANA.]¶

This document (RFCXXXX) is the reference for the registration described in this section.¶

A new chunk parameter type has to be assigned by IANA. This requires an additional line in the "Chunk Parameter Types" registry for SCTP:¶

7. Security Considerations

This document does not change the considerations given in [RFC9260].¶

8. References