draft-ietf-tsvwg-natsupp-07.txt   draft-ietf-tsvwg-natsupp-08.txt 
Network Working Group R. Stewart Network Working Group R. Stewart
Internet-Draft Netflix, Inc. Internet-Draft Netflix, Inc.
Intended status: Standards Track M. Tuexen Intended status: Standards Track M. Tuexen
Expires: August 29, 2015 I. Ruengeler Expires: January 6, 2016 I. Ruengeler
Muenster Univ. of Appl. Sciences Muenster Univ. of Appl. Sciences
February 25, 2015 July 5, 2015
Stream Control Transmission Protocol (SCTP) Network Address Translation Stream Control Transmission Protocol (SCTP) Network Address Translation
Support Support
draft-ietf-tsvwg-natsupp-07.txt draft-ietf-tsvwg-natsupp-08.txt
Abstract Abstract
Stream Control Transmission Protocol [RFC4960] 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
TCP [RFC0793]. With the widespread deployment of Network Address the Transmission Control Protocol (TCP). With the widespread
Translators (NAT), specialized code has been added to NAT for TCP deployment of Network Address Translators (NAT), specialized code has
that allows multiple hosts to reside behind a NAT and yet use only a been added to NAT for TCP that allows multiple hosts to reside behind
single globally unique IPv4 address, even when two hosts (behind a a NAT and yet use only a single globally unique IPv4 address, even
NAT) choose the same port numbers for their connection. This when two hosts (behind a NAT) choose the same port numbers for their
additional code is sometimes classified as Network Address and Port connection. This additional code is sometimes classified as Network
Translation (NAPT). To date, specialized code for SCTP has not yet Address and Port Translation (NAPT).
been added to most NATs so that only pure NAT is available. The end
result of this is that only one SCTP capable host can be behind a
NAT.
This document describes the protocol extensions required for the SCTP This document describes the protocol extensions required for the SCTP
endpoints to help NATs provide similar features of NAPT in the endpoints and the mechanisms for NATs necessary to provide similar
single-point and multi-point traversal scenario. features of NAPT in the single-point and multi-point traversal
scenario.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 29, 2015. This Internet-Draft will expire on January 6, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. SCTP NAT Traversal Scenarios . . . . . . . . . . . . . . 6 4.1. SCTP NAT Traversal Scenarios . . . . . . . . . . . . . . 6
4.1.1. Single Point Traversal . . . . . . . . . . . . . . . 6 4.1.1. Single Point Traversal . . . . . . . . . . . . . . . 6
4.1.2. Multi Point Traversal . . . . . . . . . . . . . . . . 7 4.1.2. Multi Point Traversal . . . . . . . . . . . . . . . . 7
4.2. Limitations of Classical NAPT for SCTP . . . . . . . . . 7 4.2. Limitations of Classical NAPT for SCTP . . . . . . . . . 8
4.3. The SCTP Specific Variant of NAT . . . . . . . . . . . . 8 4.3. The SCTP Specific Variant of NAT . . . . . . . . . . . . 8
5. Data Formats . . . . . . . . . . . . . . . . . . . . . . . . 12 5. Data Formats . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1. Modified Chunks . . . . . . . . . . . . . . . . . . . . . 12 5.1. Modified Chunks . . . . . . . . . . . . . . . . . . . . . 12
5.1.1. Extended ABORT Chunk . . . . . . . . . . . . . . . . 12 5.1.1. Extended ABORT Chunk . . . . . . . . . . . . . . . . 12
5.1.2. Extended ERROR Chunk . . . . . . . . . . . . . . . . 12 5.1.2. Extended ERROR Chunk . . . . . . . . . . . . . . . . 13
5.2. New Error Causes . . . . . . . . . . . . . . . . . . . . 13 5.2. New Error Causes . . . . . . . . . . . . . . . . . . . . 13
5.2.1. VTag and Port Number Collision Error Cause . . . . . 13 5.2.1. VTag and Port Number Collision Error Cause . . . . . 13
5.2.2. Missing State Error Cause . . . . . . . . . . . . . . 13 5.2.2. Missing State Error Cause . . . . . . . . . . . . . . 14
5.2.3. Port Number Collision Error Cause . . . . . . . . . . 14 5.2.3. Port Number Collision Error Cause . . . . . . . . . . 15
5.3. New Parameters . . . . . . . . . . . . . . . . . . . . . 14 5.3. New Parameters . . . . . . . . . . . . . . . . . . . . . 15
5.3.1. Disable Restart Parameter . . . . . . . . . . . . . . 14 5.3.1. Disable Restart Parameter . . . . . . . . . . . . . . 16
5.3.2. VTags Parameter . . . . . . . . . . . . . . . . . . . 15 5.3.2. VTags Parameter . . . . . . . . . . . . . . . . . . . 16
6. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 16 6. Procedures for SCTP End Points and NATs . . . . . . . . . . . 17
6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 16 6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 17
6.2. Association Setup Considerations . . . . . . . . . . . . 17 6.2. Association Setup Considerations . . . . . . . . . . . . 18
6.3. Handling of Internal Port Number and Verification Tag 6.3. Handling of Internal Port Number and Verification Tag
Collisions . . . . . . . . . . . . . . . . . . . . . . . 17 Collisions . . . . . . . . . . . . . . . . . . . . . . . 18
6.4. Handling of Internal Port Number Collisions . . . . . . . 18 6.4. Handling of Internal Port Number Collisions . . . . . . . 19
6.5. Handling of Missing State . . . . . . . . . . . . . . . . 19 6.5. Handling of Missing State . . . . . . . . . . . . . . . . 20
6.6. Handling of Fragmented SCTP Packets . . . . . . . . . . . 21 6.6. Handling of Fragmented SCTP Packets . . . . . . . . . . . 22
6.7. Multi-Point Traversal Considerations . . . . . . . . . . 21 6.7. Multi-Point Traversal Considerations . . . . . . . . . . 22
7. Various Examples of NAT Traversals . . . . . . . . . . . . . 21 7. Various Examples of NAT Traversals . . . . . . . . . . . . . 22
7.1. Single-homed Client to Single-homed Server . . . . . . . 21 7.1. Single-homed Client to Single-homed Server . . . . . . . 22
7.2. Single-homed Client to Multi-homed Server . . . . . . . . 23 7.2. Single-homed Client to Multi-homed Server . . . . . . . . 25
7.3. Multihomed Client and Server . . . . . . . . . . . . . . 26 7.3. Multihomed Client and Server . . . . . . . . . . . . . . 28
7.4. NAT Loses Its State . . . . . . . . . . . . . . . . . . . 30 7.4. NAT Loses Its State . . . . . . . . . . . . . . . . . . . 32
7.5. Peer-to-Peer Communication . . . . . . . . . . . . . . . 32 7.5. Peer-to-Peer Communication . . . . . . . . . . . . . . . 34
8. Socket API Considerations . . . . . . . . . . . . . . . . . . 37 8. Socket API Considerations . . . . . . . . . . . . . . . . . . 39
8.1. Get or Set the NAT Friendliness 8.1. Get or Set the NAT Friendliness
(SCTP_NAT_FRIENDLY) . . . . . . . . . . . . . . . . . . . 38 (SCTP_NAT_FRIENDLY) . . . . . . . . . . . . . . . . . . . 40
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40
9.1. New Chunk Flags for Two Existing Chunk Types . . . . . . 38 9.1. New Chunk Flags for Two Existing Chunk Types . . . . . . 40
9.2. Three New Error Causes . . . . . . . . . . . . . . . . . 39 9.2. Three New Error Causes . . . . . . . . . . . . . . . . . 41
9.3. Two New Chunk Parameter Types . . . . . . . . . . . . . . 40 9.3. Two New Chunk Parameter Types . . . . . . . . . . . . . . 42
10. Security Considerations . . . . . . . . . . . . . . . . . . . 40 10. Security Considerations . . . . . . . . . . . . . . . . . . . 42
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 40 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 42
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 41 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 43
12.1. Normative References . . . . . . . . . . . . . . . . . . 41 12.1. Normative References . . . . . . . . . . . . . . . . . . 43
12.2. Informative References . . . . . . . . . . . . . . . . . 41 12.2. Informative References . . . . . . . . . . . . . . . . . 43
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43
1. Introduction 1. Introduction
Stream Control Transmission Protocol [RFC4960] provides a reliable Stream Control Transmission Protocol [RFC4960] 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
TCP [RFC0793]. With the widespread deployment of Network Address TCP [RFC0793]. With the widespread deployment of Network Address
Translators (NAT), specialized code has been added to NAT for TCP Translators (NAT), specialized code has been added to NAT for TCP
that allows multiple hosts to reside behind a NAT using private that allows multiple hosts to reside behind a NAT using private
addresses (see [RFC6890]) and yet use only a single globally unique addresses (see [RFC6890]) and yet use only a single globally unique
IPv4 address, even when two hosts (behind a NAT) choose the same port IPv4 address, even when two hosts (behind a NAT) choose the same port
numbers for their connection. This additional code is sometimes numbers for their connection. This additional code is sometimes
classified as Network Address and Port Translation (NAPT). To date, classified as Network Address and Port Translation (NAPT). Please
note that this document focuses on the case where the NAT maps
multiple private addresses to a single public address. To date,
specialized code for SCTP has not yet been added to most NATs so that specialized code for SCTP has not yet been added to most NATs so that
only true NAT is available. The end result of this is that only one only true NAT is available. The end result of this is that only one
SCTP capable host can be behind a NAT. SCTP capable host can be behind a NAT. The only alternative for
supporting legacy NATs is to use UDP encapsulation as specified in
[RFC6951].
This document describes an SCTP specific variant NAT and specific This document describes an SCTP specific variant NAT and specific
packets and procedures to help NATs provide similar features of NAPT packets and procedures to help NATs provide similar features of NAPT
in the single-point and multi-point traversal scenario. An SCTP in the single-point and multi-point traversal scenario. An SCTP
implementation supporting this extension will follow these procedures implementation supporting this extension will follow these procedures
to assure that in both single-homed and multi-homed cases a NAT will to assure that in both single-homed and multi-homed cases a NAT will
maintain the proper state without needing to change port numbers. maintain the proper state without needing to change port numbers.
The authors feel it is possible and desirable to make these changes It is possible and desirable to make these changes for a number of
for a number of reasons: reasons:
o It is desirable for SCTP internal end-hosts on multiple platforms o It is desirable for SCTP internal end-hosts on multiple platforms
to be able to share a NAT's public IP address, much as TCP does to be able to share a NAT's public IP address in the same way that
today. a TCP session can use a NAT.
o If a NAT does not need to change any data within an SCTP packet it o If a NAT does not need to change any data within an SCTP packet it
will reduce the processing burden of NAT'ing SCTP by NOT needing will reduce the processing burden of NAT'ing SCTP by NOT needing
to execute the CRC32c checksum required by SCTP. to execute the CRC32c checksum required by SCTP.
o Not having to touch the IP payload makes the processing of ICMP o Not having to touch the IP payload makes the processing of ICMP
messages in NATs easier. messages in NATs easier.
An SCTP-aware NAT will need to follow these procedures for generating An SCTP-aware NAT will need to follow these procedures for generating
appropriate SCTP packet formats. appropriate SCTP packet formats.
skipping to change at page 4, line 38 skipping to change at page 4, line 42
| No Support | Support | Support | Limited | | No Support | Support | Support | Limited |
| No Support | Support | No Support | Limited | | No Support | Support | No Support | Limited |
| No Support | No Support | Support | None | | No Support | No Support | Support | None |
| No Support | No Support | No Support | None | | No Support | No Support | No Support | None |
+---------------+------------+---------------+---------------+ +---------------+------------+---------------+---------------+
Table 1: Communication possibilities Table 1: Communication possibilities
From the table we can see that when a NAT does not support the From the table we can see that when a NAT does not support the
extension no communication can occur. This is because for the most extension no communication can occur. This is because for the most
part of the current situation i. e. SCTP packets sent externally part of the current situation i.e. SCTP packets sent externally from
from behind a NAT are discarded by the NAT. In some cases, where the behind a NAT are discarded by the NAT. In some cases, where the NAT
NAT supports the feature but one of the two external hosts does not supports the feature but one of the two external hosts does not
support the feature, communication may occur but in a limited way. support the feature, communication may occur but in a limited way.
For example only one host may be able to have a connection when a For example only one host may be able to have a connection when a
collision case occurs. collision case occurs.
2. Conventions 2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Terminology 3. Terminology
This document uses the following terms, which are depicted in This document uses the following terms, which are depicted in
Figure 1. Figure 1. Familiarity with the terminology used in [RFC4960] and
[RFC5061] is assumed.
Private-Address (Priv-Addr): The private address that is known to Private-Address (Priv-Addr): The private address that is known to
the internal host. the internal host.
Internal-Port (Int-Port): The port number that is in use by the host Internal-Port (Int-Port): The port number that is in use by the host
holding the Private-Address. holding the Private-Address.
Internal-VTag (Int-VTag): The Verification Tag that the internal Internal-VTag (Int-VTag): The SCTP Verification Tag (VTag) that the
host has chosen for its communication. The VTag is a unique internal host has chosen for its communication. The VTag is a
32-bit tag that must accompany any incoming SCTP packet for this unique 32-bit tag that must accompany any incoming SCTP packet for
association to the Private-Address. this association to the Private-Address.
External-Address (Ext-Addr): The address that an internal host is External-Address (Ext-Addr): The address that an internal host is
attempting to contact. attempting to contact.
External-Port (Ext-Port): The port number of the peer process at the External-Port (Ext-Port): The port number of the peer process at the
External-Address. External-Address.
External-VTag (Ext-VTag): The Verification Tag that the host holding External-VTag (Ext-VTag): The Verification Tag that the host holding
the External-Address has chosen for its communication. The VTag the External-Address has chosen for its communication. The VTag
is a unique 32-bit tag that must accompany any incoming SCTP is a unique 32-bit tag that must accompany any incoming SCTP
skipping to change at page 7, line 36 skipping to change at page 8, line 11
can preserve the path diversity of a multi-homed association for the can preserve the path diversity of a multi-homed association for the
entire path. This in turn can improve the robustness of the entire path. This in turn can improve the robustness of the
communication. communication.
4.2. Limitations of Classical NAPT for SCTP 4.2. Limitations of Classical NAPT for SCTP
Using classical NAPT may result in changing one of the SCTP port Using classical NAPT may result in changing one of the SCTP port
numbers during the processing which requires the recomputation of the numbers during the processing which requires the recomputation of the
transport layer checksum. Whereas for UDP and TCP this can be done transport layer checksum. Whereas for UDP and TCP this can be done
very efficiently, for SCTP the checksum (CRC32c) over the entire very efficiently, for SCTP the checksum (CRC32c) over the entire
packet needs to be recomputed. This would add considerable to the packet needs to be recomputed. This would considerably add to the
NAT computational burden, however hardware support may mitigate this NAT computational burden, however hardware support may mitigate this
in some implementations. in some implementations.
An SCTP endpoint may have multiple addresses but only has a single An SCTP endpoint may have multiple addresses but only has a single
port number. To make multipoint traversal work, all the NATs port number. To make multipoint traversal work, all the NATs
involved must recognize the packets they see as belonging to the same involved must recognize the packets they see as belonging to the same
SCTP association and perform port number translation in a consistent SCTP association and perform port number translation in a consistent
way. One possible way of doing this is to use pre-defined table of way. One possible way of doing this is to use pre-defined table of
ports and addresses configured within each NAT. Other mechanisms ports and addresses configured within each NAT. Other mechanisms
could make use of NAT to NAT communication. Such mechanisms are could make use of NAT to NAT communication. Such mechanisms are not
considered by the authors not to be deployable on a wide scale base to be deployable on a wide scale base and thus not a recommended
and thus not a recommended solution. Therefore the SCTP variant of solution. Therefore the SCTP variant of NAT has been developed.
NAT has been developed.
4.3. The SCTP Specific Variant of NAT 4.3. The SCTP Specific Variant of NAT
In this section we assume that we have multiple SCTP capable hosts In this section we assume that we have multiple SCTP capable hosts
behind a NAT which has one Public-Address. Furthermore we are behind a NAT which has one Public-Address. Furthermore we are
focusing in this section on the single point traversal scenario. focusing in this section on the single point traversal scenario.
The modification of SCTP packets sent to the public Internet is easy. The modification of SCTP packets sent to the public Internet is easy.
The source address of the packet has to be replaced with the Public- The source address of the packet has to be replaced with the Public-
Address. It may also be necessary to establish some state in the NAT Address. It may also be necessary to establish some state in the NAT
skipping to change at page 9, line 24 skipping to change at page 9, line 32
Create(Initiate-Tag, Int-Port, Priv-Addr, 0) Create(Initiate-Tag, Int-Port, Priv-Addr, 0)
Returns(NAT-State control block) Returns(NAT-State control block)
Translate To: Translate To:
INIT[Initiate-Tag] INIT[Initiate-Tag]
Pub-Addr:Int-Port ------> Ext-Addr:Ext-Port Pub-Addr:Int-Port ------> Ext-Addr:Ext-Port
Ext-VTag=0 Ext-VTag=0
It should be noted that normally a NAT control block will be created. Normally a NAT control block will be created. However, it is
However, it is possible that there is already a NAT control block possible that there is already a NAT control block with the same
with the same External-Address, External-Port, Internal-Port, and External-Address, External-Port, Internal-Port, and Internal-VTag but
Internal-VTag but different Private-Address. In this case the INIT different Private-Address. In this case the INIT MUST be dropped by
SHOULD be dropped by the NAT and an ABORT SHOULD be sent back to the the NAT and an ABORT MUST be sent back to the SCTP host with the
SCTP host with the M-Bit set and an appropriate error cause (see M-Bit set and an appropriate error cause (see Section 5.1.1 for the
Section 5.1.1 for the format). The source address of the packet format). The source address of the packet containing the ABORT chunk
containing the ABORT chunk MUST be the destination address of the MUST be the destination address of the packet containing the INIT
packet containing the INIT chunk. chunk.
It is also possible that a connection to External-Address and It is also possible that a connection to External-Address and
External-Port exists without an Internal-VTag conflict but the External-Port exists without an Internal-VTag conflict but the
External-Address does not support the DISABLE_RESTART feature (noted External-Address does not support the DISABLE_RESTART feature (noted
in the NAT control block when the prior connection was established). in the NAT control block when the prior connection was established).
In such a case the INIT SHOULD be dropped by the NAT and an ABORT In such a case the INIT SHOULD be dropped by the NAT and an ABORT
SHOULD be sent back to the SCTP host with the M-Bit set and an SHOULD be sent back to the SCTP host with the M-Bit set and an
appropriate error cause (see Section 5.1.1 for the format). appropriate error cause (see Section 5.1.1 for the format).
The processing of outgoing SCTP packets containing no INIT-chunk is The processing of outgoing SCTP packets containing no INIT-chunk is
skipping to change at page 12, line 14 skipping to change at page 12, line 30
For an incoming packet containing an INIT-chunk a table lookup is For an incoming packet containing an INIT-chunk a table lookup is
made only based on the addresses and port numbers. If an entry with made only based on the addresses and port numbers. If an entry with
an External-VTag of zero is found, it is considered a match and the an External-VTag of zero is found, it is considered a match and the
External-VTag is updated. External-VTag is updated.
This allows the handling of INIT-collision through NAT. This allows the handling of INIT-collision through NAT.
5. Data Formats 5. Data Formats
This section defines the formats used to support NAT traversal.
Section 5.1 and Section 5.2 describe chunks and error causes sent by
NATs and received by SCTP end points. Section 5.3 describes
parameters sent by SCTP end points and used by NATs and SCTP end
points.
5.1. Modified Chunks 5.1. Modified Chunks
This section presents existing chunks defined in [RFC4960] that are This section presents existing chunks defined in [RFC4960] that are
modified by this document. modified by this document.
5.1.1. Extended ABORT Chunk 5.1.1. Extended ABORT Chunk
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 12, line 30 skipping to change at page 13, line 4
0 1 2 3 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 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 = 6 | Reserved |M|T| Length | | Type = 6 | Reserved |M|T| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \ \ \
/ zero or more Error Causes / / zero or more Error Causes /
\ \ \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The ABORT chunk is extended to add the new 'M-bit'. The M-bit The ABORT chunk is extended to add the new 'M-bit'. The M-bit
indicates to the receiver of the ABORT chunk that the chunk was not indicates to the receiver of the ABORT chunk that the chunk was not
generated by the peer SCTP endpoint, but instead by a middle box. generated by the peer SCTP endpoint, but instead by a middle box.
[NOTE:
ASSIGNMENT OF M-BIT TO BE CONFIRMED BY IANA.
]
5.1.2. Extended ERROR Chunk 5.1.2. Extended ERROR Chunk
0 1 2 3 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 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 = 9 | Reserved |M|T| Length | | Type = 9 | Reserved |M|T| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \ \ \
/ zero or more Error Causes / / zero or more Error Causes /
\ \ \ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The ERROR chunk defined in [RFC4960] is extended to add the new The ERROR chunk defined in [RFC4960] is extended to add the new
'M-bit'. The M-bit indicates to the receiver of the ERROR chunk that 'M-bit'. The M-bit indicates to the receiver of the ERROR chunk that
the chunk was not generated by the peer SCTP endpoint, but instead by the chunk was not generated by the peer SCTP endpoint, but instead by
a middle box. a middle box.
[NOTE:
ASSIGNMENT OF M-BIT TO BE CONFIRMED BY IANA.
]
5.2. New Error Causes 5.2. New Error Causes
This section defines the new error causes added by this document. This section defines the new error causes added by this document.
5.2.1. VTag and Port Number Collision Error Cause 5.2.1. VTag and Port Number Collision Error Cause
0 1 2 3 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 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 = 0x00B0 | Cause Length = Variable | | Cause Code = 0x00B0 | Cause Length = Variable |
skipping to change at page 13, line 36 skipping to change at page 14, line 20
This field holds the length in bytes of the error cause. The This field holds the length in bytes of the error cause. The
value MUST be the length of the Cause-Specific Information plus 4. value MUST be the length of the Cause-Specific Information plus 4.
Chunk: variable length Chunk: variable length
The Cause-Specific Information is filled with the chunk that The Cause-Specific Information is filled with the chunk that
caused this error. This can be an INIT, INIT-ACK, or ASCONF caused this error. This can be an INIT, INIT-ACK, or ASCONF
chunk. Note that if the entire chunk will not fit in the ERROR chunk. Note that if the entire chunk will not fit in the ERROR
chunk or ABORT chunk being sent then the bytes that do not fit are chunk or ABORT chunk being sent then the bytes that do not fit are
truncated. truncated.
[NOTE:
ASSIGNMENT OF CAUSE-CODE TO BE CONFIRMED BY IANA.
]
5.2.2. Missing State Error Cause 5.2.2. Missing State Error Cause
0 1 2 3 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 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 = 0x00B1 | Cause Length = Variable | | Cause Code = 0x00B1 | Cause Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ Incoming Packet / \ Incoming Packet /
/ \ / \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 14, line 14 skipping to change at page 15, line 5
This field holds the length in bytes of the error cause. The This field holds the length in bytes of the error cause. The
value MUST be the length of the Cause-Specific Information plus 4. value MUST be the length of the Cause-Specific Information plus 4.
Incoming Packet: variable length Incoming Packet: variable length
The Cause-Specific Information is filled with the IPv4 or IPv6 The Cause-Specific Information is filled with the IPv4 or IPv6
packet that caused this error. The IPv4 or IPv6 header MUST be packet that caused this error. The IPv4 or IPv6 header MUST be
included. Note that if the packet will not fit in the ERROR chunk included. Note that if the packet will not fit in the ERROR chunk
or ABORT chunk being sent then the bytes that do not fit are or ABORT chunk being sent then the bytes that do not fit are
truncated. truncated.
[NOTE:
ASSIGNMENT OF CAUSE-CODE TO BE CONFIRMED BY IANA.
]
5.2.3. Port Number Collision Error Cause 5.2.3. Port Number Collision Error Cause
0 1 2 3 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 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 = 0x00B2 | Cause Length = Variable | | Cause Code = 0x00B2 | Cause Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ chunk / \ chunk /
/ \ / \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 14, line 41 skipping to change at page 15, line 38
This field holds the length in bytes of the error cause. The This field holds the length in bytes of the error cause. The
value MUST be the length of the Cause-Specific Information plus 4. value MUST be the length of the Cause-Specific Information plus 4.
Chunk: variable length Chunk: variable length
The Cause-Specific Information is filled with the chunk that The Cause-Specific Information is filled with the chunk that
caused this error. This can be an INIT, INIT-ACK, or ASCONF caused this error. This can be an INIT, INIT-ACK, or ASCONF
chunk. Note that if the entire chunk will not fit in the ERROR chunk. Note that if the entire chunk will not fit in the ERROR
chunk or ABORT chunk being sent then the bytes that do not fit are chunk or ABORT chunk being sent then the bytes that do not fit are
truncated. truncated.
[NOTE:
ASSIGNMENT OF CAUSE-CODE TO BE CONFIRMED BY IANA.
]
5.3. New Parameters 5.3. New Parameters
This section defines new parameters and their valid appearance This section defines new parameters and their valid appearance
defined by this document. defined by this document.
5.3.1. Disable Restart Parameter 5.3.1. Disable Restart Parameter
This parameter is used to indicate that the RESTART procedure is This parameter is used to indicate that the RESTART procedure is
requested to be disabled. Both endpoints of an association MUST requested to be disabled. Both endpoints of an association MUST
include this parameter in the INIT chunk and INIT-ACK chunk when include this parameter in the INIT chunk and INIT-ACK chunk when
skipping to change at page 15, line 22 skipping to change at page 16, line 28
Parameter Type: 2 bytes (unsigned integer) Parameter Type: 2 bytes (unsigned integer)
This field holds the IANA defined parameter type for the Disable This field holds the IANA defined parameter type for the Disable
Restart Parameter. The suggested value of this field for IANA is Restart Parameter. The suggested value of this field for IANA is
0xC007. 0xC007.
Parameter Length: 2 bytes (unsigned integer) Parameter Length: 2 bytes (unsigned integer)
This field holds the length in bytes of the parameter. The value This field holds the length in bytes of the parameter. The value
MUST be 4. MUST be 4.
[NOTE:
ASSIGNMENT OF PARAMETER TYPE TO BE CONFIRMED BY IANA.
]
This parameter MAY appear in INIT, INIT-ACK and ASCONF chunks and This parameter MAY appear in INIT, INIT-ACK and ASCONF chunks and
MUST NOT appear in any other chunk. MUST NOT appear in any other chunk.
5.3.2. VTags Parameter 5.3.2. VTags Parameter
This parameter is used to help a NAT recover from state loss. This parameter is used to help a NAT recover from state loss.
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 16, line 22 skipping to change at page 17, line 33
communication. The Verification Tag is a unique 32-bit tag that communication. The Verification Tag is a unique 32-bit tag that
must accompany any incoming SCTP packet for this association to must accompany any incoming SCTP packet for this association to
the Private-Address. the Private-Address.
External Verification Tag: 4 bytes (unsigned integer) The External Verification Tag: 4 bytes (unsigned integer) The
Verification Tag that the host holding the External-Address has Verification Tag that the host holding the External-Address has
chosen for its communication. The VTag is a unique 32-bit tag chosen for its communication. The VTag is a unique 32-bit tag
that must accompany any incoming SCTP packet for this association that must accompany any incoming SCTP packet for this association
to the External-Address. to the External-Address.
[NOTE:
ASSIGNMENT OF PARAMETER TYPE TO BE CONFIRMED BY IANA.
]
This parameter MAY appear in ASCONF chunks and MUST NOT appear in any This parameter MAY appear in ASCONF chunks and MUST NOT appear in any
other chunk. other chunk.
6. Procedures 6. Procedures for SCTP End Points and NATs
6.1. Overview 6.1. Overview
When an SCTP endpoint is behind an SCTP-aware NAT a number of When an SCTP endpoint is behind an SCTP-aware NAT a number of
problems may arise as it tries to communicate with its peer: problems may arise as it tries to communicate with its peer:
o More than one host behind a NAT may pick the same VTag and source o More than one host behind a NAT may pick the same VTag and source
port when talking to the same peer server. This creates a port when talking to the same peer server. This creates a
situation where the NAT will not be able to tell the two situation where the NAT will not be able to tell the two
associations apart. This situation is discussed in Section 6.3. associations apart. This situation is discussed in Section 6.3.
skipping to change at page 16, line 50 skipping to change at page 18, line 20
discussed in Section 6.4. discussed in Section 6.4.
o A restart of a NAT during a conversation could cause a loss of its o A restart of a NAT during a conversation could cause a loss of its
state. This problem and its solution is discussed in Section 6.5. state. This problem and its solution is discussed in Section 6.5.
o An SCTP endpoint may be behind two NATs providing redundancy. The o An SCTP endpoint may be behind two NATs providing redundancy. The
method to set up this scenario is discussed in Section 6.7. method to set up this scenario is discussed in Section 6.7.
Each of these mechanisms requires additional chunks and parameters, Each of these mechanisms requires additional chunks and parameters,
defined in this document, and possibly modified handling procedures defined in this document, and possibly modified handling procedures
from those specified in [RFC4960] fdafdfafdafdafdafdafdasf. from those specified in [RFC4960].
6.2. Association Setup Considerations 6.2. Association Setup Considerations
The association setup procedure defined in [RFC4960] allows multi-
homed SCTP end points to exchange its IP-addresses by using IPv4 or
IPv6 address parameters in the INIT and INIT-ACK chunks. However,
this can't be used when NATs are present.
Every association MUST initially be set up single-homed. There MUST Every association MUST initially be set up single-homed. There MUST
NOT be any IPv4 Address parameter, IPv6 Address parameter, or NOT be any IPv4 Address parameter, IPv6 Address parameter, or
Supported Address Types parameter in the INIT-chunk. The INIT-ACK Supported Address Types parameter in the INIT-chunk. The INIT-ACK
chunk MUST NOT contain any IPv4 Address parameter or IPv6 Address chunk MUST NOT contain any IPv4 Address parameter or IPv6 Address
parameter. parameter.
If the association should finally be multi-homed, the procedure in If the association should finally be multi-homed, the procedure in
Section 6.7 MUST be used. Section 6.7 MUST be used.
The INIT and INIT-ACK chunk SHOULD contain the Disable Restart The INIT and INIT-ACK chunk SHOULD contain the Disable Restart
skipping to change at page 17, line 29 skipping to change at page 18, line 51
6.3. Handling of Internal Port Number and Verification Tag Collisions 6.3. Handling of Internal Port Number and Verification Tag Collisions
Consider the case where two hosts in the Private-Address space want Consider the case where two hosts in the Private-Address space want
to set up an SCTP association with the same server running on the to set up an SCTP association with the same server running on the
same host in the Internet. This means that the External-Port and the same host in the Internet. This means that the External-Port and the
External-Address are the same. If they both choose the same External-Address are the same. If they both choose the same
Internal-Port and Internal-VTag, the NAT box cannot distinguish Internal-Port and Internal-VTag, the NAT box cannot distinguish
between incoming packets anymore. But this is very unlikely. The between incoming packets anymore. But this is very unlikely. The
Internal-VTags are chosen at random and if the Internal-Ports are Internal-VTags are chosen at random and if the Internal-Ports are
also chosen from the ephemeral port range at random this gives a also chosen from the ephemeral port range at random this gives a
46-bit random number which has to match. In the TCP like NAPT case 46-bit random number which has to match. In the TCP-like NAPT case
the NAT box can control the 16-bit Natted Port and therefor avoid the NAT box can control the 16-bit Natted Port and therefore avoid
collisions deterministically. collisions deterministically.
The same can happen when an INIT-ACK chunk or an ASCONF chunk is The same can happen when an INIT-ACK chunk or an ASCONF chunk is
processed by the NAT. processed by the NAT.
However, in this unlikely event the NAT box MUST send an ABORT chunk However, in this unlikely event the NAT box MUST send an ABORT chunk
with the M-bit set if the collision is triggered by an INIT or INIT- with the M-bit set if the collision is triggered by an INIT or INIT-
ACK chunk or send an ERROR chunk with the M-bit set if the collision ACK chunk or send an ERROR chunk with the M-bit set if the collision
is triggered by an ASCONF chunk. The M-bit is a new bit defined by is triggered by an ASCONF chunk. The M-bit is a new bit defined by
this document to express to SCTP that the source of this packet is a this document to express to SCTP that the source of this packet is a
"middle" box, not the peer SCTP endpoint (see Section 5.1.1). If a "middle" box, not the peer SCTP endpoint (see Section 5.1.1). If a
packet containing an INIT-ACK chunk triggers the collision, the packet containing an INIT-ACK chunk triggers the collision, the
corresponding packet containing the ABORT chunk MUST contain the same corresponding packet containing the ABORT chunk MUST contain the same
source and destination address and port numbers as the packet source and destination address and port numbers as the packet
containing the INIT-ACK chunk. In the other two cases, the source containing the INIT-ACK chunk. In the other two cases, the source
and destination address and port numbers MUST be swapped. and destination address and port numbers MUST be swapped.
The sender of the packet containing the INIT chunk or the receiver of The sender of the packet containing the INIT chunk or the receiver of
the INIT-ACK chunk, upon reception of an ABORT chunk with M-bit set, the INIT-ACK chunk, upon reception of an ABORT chunk with M-bit set
SHOULD reinitiate the association setup procedure after choosing a and the appropriate error cause code for colliding NAT table state is
new initiate tag. These procedures SHOULD be followed only if the included, MUST reinitiate the association setup procedure after
appropriate error cause code for colliding NAT table state is choosing a new initiate tag, if the association is in COOKIE-WAIT
included AND the association is in the COOKIE-WAIT state (i. e. it is state. In any other state, the SCTP endpoint MUST NOT respond.
awaiting an INIT-ACK). If the endpoint is in any other state an SCTP
endpoint SHOULD NOT respond.
The sender of the ASCONF chunk, upon reception of an ERROR chunk with The sender of the ASCONF chunk, upon reception of an ERROR chunk with
M-bit set, MUST stop adding the path to the association. M-bit set, MUST stop adding the path to the association.
The sender of the ERROR or ABORT chunk MUST include the error cause The sender of the ERROR or ABORT chunk MUST include the error cause
with cause code 'VTag and Port Number Collision' (see Section 5.2.1). with cause code 'VTag and Port Number Collision' (see Section 5.2.1).
6.4. Handling of Internal Port Number Collisions 6.4. Handling of Internal Port Number Collisions
When two SCTP hosts are behind an SCTP-aware NAT it is possible that When two SCTP hosts are behind an SCTP-aware NAT it is possible that
two SCTP hosts in the Private-Address space will want to set up an two SCTP hosts in the Private-Address space will want to set up an
SCTP association with the same server running on the same host in the SCTP association with the same server running on the same host in the
Internet. For the NAT appropriate tracking may be performed by Internet. For the NAT, appropriate tracking may be performed by
assuring that the VTags are unique between the two hosts. But for assuring that the VTags are unique between the two hosts.
the external SCTP server on the internet this means that the
But for the external SCTP server on the Internet this means that the
External-Port and the External-Address are the same. If they both External-Port and the External-Address are the same. If they both
have chosen the same Internal-Port the server cannot distinguish have chosen the same Internal-Port the server cannot distinguish
between both associations based on the address and port numbers. For between both associations based on the address and port numbers. For
the server it looks like the association is being restarted. To the server it looks like the association is being restarted. To
overcome this limitation the client sends a Disable Restart parameter overcome this limitation the client sends a Disable Restart parameter
in the INIT-chunk. in the INIT-chunk.
When the server receives this parameter it MUST do the following: When the server receives this parameter it MUST do the following:
o Include a Disable Restart parameter in the INIT-ACK to inform the o Include a Disable Restart parameter in the INIT-ACK to inform the
skipping to change at page 18, line 43 skipping to change at page 20, line 17
o Disable the restart procedures defined in [RFC4960] for this o Disable the restart procedures defined in [RFC4960] for this
association. association.
Servers that support this feature will need to be capable of Servers that support this feature will need to be capable of
maintaining multiple connections to what appears to be the same peer maintaining multiple connections to what appears to be the same peer
(behind the NAT) differentiated only by the VTags. (behind the NAT) differentiated only by the VTags.
The NAT, when processing the INIT-ACK, should note in its internal The NAT, when processing the INIT-ACK, should note in its internal
table that the association supports the Disable Restart extension. table that the association supports the Disable Restart extension.
This note is used when establishing future associations (i. e. when This note is used when establishing future associations (i.e. when
processing an INIT from an internal host) to decide if the connection processing an INIT from an internal host) to decide if the connection
should be allowed. The NAT MUST do the following when processing an should be allowed. The NAT MUST do the following when processing an
INIT: INIT:
o If the INIT is destined to an external address and port for which o If the INIT is destined to an external address and port for which
the NAT has no outbound connection, allow the INIT creating an the NAT has no outbound connection, allow the INIT creating an
internal mapping table. internal mapping table.
o If the INIT matches the external address and port of an already o If the INIT matches the external address and port of an already
existing connection, validate that the external server supports existing connection, validate that the external server supports
skipping to change at page 20, line 37 skipping to change at page 22, line 9
examination of the association is required. The endpoint MUST do the examination of the association is required. The endpoint MUST do the
following: following:
o Validate that the verification tag is reflected by looking at the o Validate that the verification tag is reflected by looking at the
VTag that would have been included in the outgoing packet. VTag that would have been included in the outgoing packet.
o Validate that the peer of the SCTP association supports the o Validate that the peer of the SCTP association supports the
dynamic address extension, if it does not discard the incoming dynamic address extension, if it does not discard the incoming
ERROR chunk. ERROR chunk.
o If the association is attempting to add an address (i. e. o If the association is attempting to add an address (i.e. following
following the procedures in Section 6.7) then the endpoint MUST- the procedures in Section 6.7) then the endpoint MUST-NOT consider
NOT consider the address part of the association and SHOULD make the address part of the association and SHOULD make no further
no further attempt to add the address (i. e. cancel any ASCONF attempt to add the address (i.e. cancel any ASCONF timers and
timers and remove any record of the path), since the NAT has a remove any record of the path), since the NAT has a VTag collision
VTag collision and the association cannot easily create a new VTag and the association cannot easily create a new VTag (as it would
(as it would if the error occurred when sending an INIT). if the error occurred when sending an INIT).
o If the endpoint has no other path, i. e. the procedure was o If the endpoint has no other path, i. e. the procedure was
executed due to missing a state in the NAT, then the endpoint MUST executed due to missing a state in the NAT, then the endpoint MUST
abort the association. This would occur only if the local NAT abort the association. This would occur only if the local NAT
restarted and accepted a new association before attempting to restarted and accepted a new association before attempting to
repair the missing state (Note that this is no different than what repair the missing state (Note that this is no different than what
happens to all TCP connections when a NAT looses its state). happens to all TCP connections when a NAT looses its state).
6.6. Handling of Fragmented SCTP Packets 6.6. Handling of Fragmented SCTP Packets
skipping to change at page 21, line 26 skipping to change at page 22, line 45
If a multi-homed SCTP endpoint behind a NAT connects to a peer, it If a multi-homed SCTP endpoint behind a NAT connects to a peer, it
SHOULD first set up the association single-homed with only one SHOULD first set up the association single-homed with only one
address causing the first NAT to populate its state. Then it SHOULD address causing the first NAT to populate its state. Then it SHOULD
add each IP address using ASCONF chunks sent via their respective add each IP address using ASCONF chunks sent via their respective
NATs. The address to add is the wildcard address and the lookup NATs. The address to add is the wildcard address and the lookup
address SHOULD also contain the VTags parameter and optionally the address SHOULD also contain the VTags parameter and optionally the
Disable Restart parameter as illustrated above. Disable Restart parameter as illustrated above.
7. Various Examples of NAT Traversals 7. Various Examples of NAT Traversals
Please note that this section is informational only.
7.1. Single-homed Client to Single-homed Server 7.1. Single-homed Client to Single-homed Server
The internal client starts the association with the external server The internal client starts the association with the external server
via a four-way-handshake. Host A starts by sending an INIT chunk. via a four-way-handshake. Host A starts by sending an INIT chunk.
/--\/--\ /--\/--\
+--------+ +-----+ / \ +--------+ +--------+ +-----+ / \ +--------+
| Host A | <------> | NAT | <------> | Internet | <------> | Host B | | Host A | <------> | NAT | <------> | Internet | <------> | Host B |
+--------+ +-----+ \ / +--------+ +--------+ +-----+ \ / +--------+
\--/\---/ \--/\---/
skipping to change at page 40, line 43 skipping to change at page 42, line 43
10. Security Considerations 10. Security Considerations
State maintenance within a NAT is always a subject of possible Denial State maintenance within a NAT is always a subject of possible Denial
Of Service attacks. This document recommends that at a minimum a NAT Of Service attacks. This document recommends that at a minimum a NAT
runs a timer on any SCTP state so that old association state can be runs a timer on any SCTP state so that old association state can be
cleaned up. cleaned up.
For SCTP end-points, this document does not add any additional For SCTP end-points, this document does not add any additional
security considerations to the ones given in [RFC4960], [RFC4895], security considerations to the ones given in [RFC4960], [RFC4895],
and [RFC5061]. and [RFC5061]. In particular, SCTP is protected by the verification
tags and the usage of [RFC4895] against off-path attackers.
11. Acknowledgments 11. Acknowledgments
The authors wish to thank Jason But, Bryan Ford, David Hayes, Alfred The authors wish to thank Jason But, Gorry Fairhurst, Bryan Ford,
Hines, Henning Peters, Timo Voelker, Dan Wing, and Qiaobing Xie for David Hayes, Alfred Hines, Henning Peters, Timo Voelker, Dan Wing,
their invaluable comments. and Qiaobing Xie for their invaluable comments.
12. References 12. References
12.1. Normative References 12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4895] Tuexen, M., Stewart, R., Lei, P., and E. Rescorla, [RFC4895] Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
"Authenticated Chunks for the Stream Control Transmission "Authenticated Chunks for the Stream Control Transmission
skipping to change at page 41, line 41 skipping to change at page 43, line 41
793, September 1981. 793, September 1981.
[RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V. [RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V.
Yasevich, "Sockets API Extensions for the Stream Control Yasevich, "Sockets API Extensions for the Stream Control
Transmission Protocol (SCTP)", RFC 6458, December 2011. Transmission Protocol (SCTP)", RFC 6458, December 2011.
[RFC6890] Cotton, M., Vegoda, L., Bonica, R., and B. Haberman, [RFC6890] Cotton, M., Vegoda, L., Bonica, R., and B. Haberman,
"Special-Purpose IP Address Registries", BCP 153, RFC "Special-Purpose IP Address Registries", BCP 153, RFC
6890, April 2013. 6890, April 2013.
[RFC6951] Tuexen, M. and R. Stewart, "UDP Encapsulation of Stream
Control Transmission Protocol (SCTP) Packets for End-Host
to End-Host Communication", RFC 6951, May 2013.
Authors' Addresses Authors' Addresses
Randall R. Stewart Randall R. Stewart
Netflix, Inc. Netflix, Inc.
Chapin, SC 29036 Chapin, SC 29036
US US
Email: randall@lakerest.net Email: randall@lakerest.net
Michael Tuexen Michael Tuexen
Muenster University of Applied Sciences Muenster University of Applied Sciences
 End of changes. 44 change blocks. 
106 lines changed or deleted 166 lines changed or added

This html diff was produced by rfcdiff 1.42. The latest version is available from http://tools.ietf.org/tools/rfcdiff/