draft-ietf-tsvwg-natsupp-18.txt   draft-ietf-tsvwg-natsupp-19.txt 
Network Working Group R. R. Stewart Network Working Group R. R. Stewart
Internet-Draft Netflix, Inc. Internet-Draft Netflix, Inc.
Intended status: Standards Track M. Tüxen Intended status: Standards Track M. Tüxen
Expires: 29 January 2021 I. Rüngeler Expires: 29 January 2021 I. Rüngeler
Münster Univ. of Appl. Sciences Münster Univ. of Appl. Sciences
28 July 2020 28 July 2020
Stream Control Transmission Protocol (SCTP) Network Address Translation Stream Control Transmission Protocol (SCTP) Network Address Translation
Support Support
draft-ietf-tsvwg-natsupp-18 draft-ietf-tsvwg-natsupp-19
Abstract Abstract
The Stream Control Transmission Protocol (SCTP) provides a reliable The Stream Control Transmission Protocol (SCTP) provides a reliable
communications channel between two end-hosts in many ways similar to communications channel between two end-hosts in many ways similar to
the Transmission Control Protocol (TCP). With the widespread the Transmission Control Protocol (TCP). With the widespread
deployment of Network Address Translators (NAT), specialized code has deployment of Network Address Translators (NAT), specialized code has
been added to NAT functions for TCP that allows multiple hosts to been added to NAT functions for TCP that allows multiple hosts to
reside behind a NAT function and yet share a single IPv4 address, reside behind a NAT function and yet share a single IPv4 address,
even when two hosts (behind a NAT function) choose the same port even when two hosts (behind a NAT function) choose the same port
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SCTP minimizes the use of IP-level fragmentation. However, it can SCTP minimizes the use of IP-level fragmentation. However, it can
happen that using IP-level fragmentation is needed to continue an happen that using IP-level fragmentation is needed to continue an
SCTP association. For example, if the path MTU is reduced and there SCTP association. For example, if the path MTU is reduced and there
are still some DATA chunk in flight, which require packets larger are still some DATA chunk in flight, which require packets larger
than the new path MTU. If IP-level fragmentation can not be used, than the new path MTU. If IP-level fragmentation can not be used,
the SCTP association will be terminated in a non-graceful way. the SCTP association will be terminated in a non-graceful way.
Therefore, a NAT function MUST be able to handle IP-level fragmented Therefore, a NAT function MUST be able to handle IP-level fragmented
SCTP packets. The fragments may arrive in any order. SCTP packets. The fragments may arrive in any order.
When an SCTP packet has to be fragmented by the NAT function and the When an SCTP packet can not be forwarded by the NAT function due to
IP header forbids fragmentation, the NAT MUST send back a MTU issues and the IP header forbids fragmentation, the NAT MUST send
corresponding ICMP message to the internal host. This allows for a back a "Fragmentation needed and DF set" ICMPv4 or PTB ICMPv6 message
faster recovery from this packet drop. to the internal host. This allows for a faster recovery from this
packet drop.
6.6. Multi Point Traversal Considerations for Endpoints 6.6. Multi Point Traversal Considerations for Endpoints
If a multi-homed SCTP endpoint behind a NAT function connects to a If a multi-homed SCTP endpoint behind a NAT function connects to a
peer, it MUST first set up the association single-homed with only one peer, it MUST first set up the association single-homed with only one
address causing the first NAT function to populate its state. Then address causing the first NAT function to populate its state. Then
it SHOULD add each IP address using packets containing ASCONF chunks it SHOULD add each IP address using packets containing ASCONF chunks
sent via their respective NAT functions. The address to add is the sent via their respective NAT functions. The address to add is the
wildcard address and the lookup address SHOULD also contain the VTags wildcard address and the lookup address SHOULD also contain the VTags
parameter and optionally the Disable Restart parameter. parameter and optionally the Disable Restart parameter.
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