draft-ietf-tsvwg-natsupp-01.txt   draft-ietf-tsvwg-natsupp-02.txt 
Network Working Group R. Stewart Network Working Group R. Stewart
Internet-Draft Adara Networks Internet-Draft Adara Networks
Intended status: Standards Track M. Tuexen Intended status: Standards Track M. Tuexen
Expires: December 3, 2011 I. Ruengeler Expires: September 13, 2012 I. Ruengeler
Muenster Univ. of Applied Muenster Univ. of Appl. Sciences
Sciences March 12, 2012
June 1, 2011
Stream Control Transmission Protocol (SCTP) Network Address Translation Stream Control Transmission Protocol (SCTP) Network Address Translation
Support Support
draft-ietf-tsvwg-natsupp-01.txt draft-ietf-tsvwg-natsupp-02.txt
Abstract Abstract
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 and yet use only a that allows multiple hosts to reside behind a NAT and yet use only a
single globally unique IPv4 address, even when two hosts (behind a single globally unique IPv4 address, even when two hosts (behind a
NAT) choose the same port numbers for their connection. This NAT) choose the same port numbers for their connection. This
additional code is sometimes classified as Network Address and Port additional code is sometimes classified as Network Address and Port
Translation or NAPT. To date, specialized code for SCTP has NOT yet Translation (NAPT). To date, specialized code for SCTP has not yet
been added to most NATs so that only pure NAT is available. The end 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 result of this is that only one SCTP capable host can be behind a
NAT. NAT.
This document describes an SCTP specific chunks and procedures to This document describes the protocol extensions required for the SCTP
help NAT's provide similar features of NAPT in the single point and endpoints to help NAT's provide similar features of NAPT in the
multi-point traversal scenario. 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 December 3, 2011. This Internet-Draft will expire on September 13, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2012 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
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publication of this document. Please review these documents publication of this document. Please review these documents
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Problem space overview . . . . . . . . . . . . . . . . . . . . 5 4. Problem Space Overview . . . . . . . . . . . . . . . . . . . . 5
5. Handling of internal port number and verification tag 5. Association Setup Considerations . . . . . . . . . . . . . . . 5
collisions . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6. Handling of Internal Port Number and Verification Tag
6. Handling of missing state . . . . . . . . . . . . . . . . . . 7 Collisions . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Multi Point Traversal considerations . . . . . . . . . . . 8 7. Handling of Internal Port Number Collisions . . . . . . . . . 7
6.2. Handling of internal port number collisions . . . . . . . 8 8. Handling of Missing State . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 9. Multi Point Traversal Considerations . . . . . . . . . . . . . 11
8. Security considerations . . . . . . . . . . . . . . . . . . . 10 10. Socket API Considerations . . . . . . . . . . . . . . . . . . 11
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 10.1. Get or Set the NAT Friendliness (SCTP_NAT_FRIENDLY) . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . . 10 11.1. New Chunk Flags for Two Chunk Types . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . . 11 11.2. Three New Error Causes . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 11.3. Two New Chunk Parameter Types . . . . . . . . . . . . . . 13
12. Security Considerations . . . . . . . . . . . . . . . . . . . 14
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
14.1. Normative References . . . . . . . . . . . . . . . . . . 14
14.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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 and yet use only a that allows multiple hosts to reside behind a NAT using private
single globally unique IPv4 address, even when two hosts (behind a addresses (see [RFC5735]) and yet use only a single globally unique
NAT) choose the same port numbers for their connection. This IPv4 address, even when two hosts (behind a NAT) choose the same port
additional code is sometimes classified as Network Address and Port numbers for their connection. This additional code is sometimes
Translation or NAPT. To date, specialized code for SCTP has NOT yet classified as Network Address and Port Translation (NAPT). To date,
been added to most NATs so that only true NAT is available. The end specialized code for SCTP has not yet been added to most NATs so that
result of this is that only one SCTP capable host can be behind a only true NAT is available. The end result of this is that only one
NAT. SCTP capable host can be behind a NAT.
This document describes an SCTP specific chunks and procedures to This document describes an SCTP specific chunks and procedures to
help NAT's provide similar features of NAPT in the single point and help NAT's provide similar features of NAPT in the single point and
multi-point traversal scenario. An SCTP implementation supporting multi-point traversal scenario. An SCTP implementation supporting
this extension will follow these procedures to assure that in both this extension will follow these procedures to assure that in both
single homed and multi-homed cases a NAT will maintian the proper single homed and multi-homed cases a NAT will maintain the proper
state without needing to change port numbers. state without needing to change port numbers.
A NAT will need to follow these proceedures for generating A NAT will need to follow these procedures for generating appropriate
appropriate SCTP packet formats. NAT's should refer to SCTP packet formats. NAT's should refer to [I-D.ietf-behave-sctpnat]
xxxxbehavedraftxxx for the BCP in using these formats. for the BCP in using these formats.
When considering this feature it is possible to have multiple levels When considering this feature it is possible to have multiple levels
of support. At each level, the Internal Host, External Host and NAT of support. At each level, the Internal Host, External Host and NAT
may or may not support the features described in this document. The may or may not support the features described in this document. The
following table illustrates the results of the various combinations following table illustrates the results of the various combinations
of support and if communications can occur between two endpoints. of support and if communications can occur between two endpoints.
+---------------+------------+---------------+---------------+ +---------------+------------+---------------+---------------+
| Internal Host | NAT | External Host | Communication | | Internal Host | NAT | External Host | Communication |
+---------------+------------+---------------+---------------+ +---------------+------------+---------------+---------------+
| Supports | Supports | Supports | Yes | | Support | Support | Support | Yes |
| Support | No Support | No Support | None | | Support | Support | No Support | Limited |
| Support | Support | No Support | Limited | | Support | No Support | Support | None |
| No Support | No Support | Support | None | | Support | No Support | No Support | None |
| Support | No Support | Support | None | | No Support | Support | Support | Limited |
| No Support | Support | Support | Limited | | No Support | Support | No Support | Limited |
| No Support | No Support | No Support | None | | No Support | No Support | Support | None |
| No Support | No Support | No Support | None |
+---------------+------------+---------------+---------------+ +---------------+------------+---------------+---------------+
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 for the most part the extension no communication can occur. This is for the most part the
current situation i.e. SCTP packets sent externally from behind a current situation i.e. SCTP packets sent externally from behind a
NAT are discarded by the NAT. In some cases, where the NAT supports NAT are discarded by the NAT. In some cases, where the NAT supports
the feature but one of the two external hosts does NOT support the the feature but one of the two external hosts does not support the
feature communication may occur but in a limited way. For example feature communication may occur but in a limited way. For example
only one host may be able to have a connection when a collision case only one host may be able to have a connection when a collision case
occurs. 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
For this discussion we will use several terms, which we will define This document uses the following terms, which are depicted in
and point out in a figure. Figure 1.
o 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.
o Internal-Port (Int-Port) - The port number that is in use by the Internal-Port (Int-Port): The port number that is in use by the host
host holding the Private-Address. holding the Private-Address.
o Internal-VTag (Int-VTag) - The Verification Tag that the internal Internal-VTag (Int-VTag): The Verification Tag that the internal
host has chosen for its communication. The VTag is a unique 32 host has chosen for its communication. The VTag is a unique 32-
bit tag that must accompany any incoming SCTP packet for this bit tag that must accompany any incoming SCTP packet for this
association to the Private-Address. association to the Private-Address.
o 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.
o External-Port (Ext-Port) - The port number of the peer process at External-Port (Ext-Port): The port number of the peer process at the
the External-Address. External-Address.
o External-VTag (Ext-VTag) - The Verification Tag that the host External-VTag (Ext-VTag): The Verification Tag that the host holding
holding the External-Address has chosen for its communication. the External-Address has chosen for its communication. The VTag
The VTag is a unique 32 bit tag that must accompany any incoming is a unique 32-bit tag that must accompany any incoming SCTP
SCTP packet for this association to the External-Address. packet for this association to the External-Address.
o Public-Address (Pub-Addr) - The public address assigned to the NAT Public-Address (Pub-Addr): The public address assigned to the NAT
box which it uses as a source address when sending packets towards box which it uses as a source address when sending packets towards
the External-Address. the External-Address.
Internal Network | External Network Internal Network | External Network
| |
Private | Public External Private | Public External
+---------+ Address | Address /--\/--\ Address +---------+ +---------+ Address | Address /--\/--\ Address +---------+
| SCTP | +-----+ / \ | SCTP | | SCTP | +-----+ / \ | SCTP |
|end point|==========| NAT |======= | Internet | ========== |end point| |end point|=========| NAT |=======| Internet |==========|end point|
| A | +-----+ \ / | B | | A | +-----+ \ / | B |
+---------+ Internal | \--/\--/ External +---------+ +---------+ Internal | \--/\--/ External+---------+
Internal Port | Port External Internal Port | Port External
VTag | VTag VTag | VTag
4. Problem space overview Figure 1: Basic network setup
When an SCTP endpoint is behind a NAT which supports xxxnatdraftxxx a 4. Problem Space Overview
number of problems may arise as it trys to communicate with its peer.
o More than one server behind a NAT may pick the same V-Tag and When an SCTP endpoint is behind a NAT which supports
[I-D.ietf-behave-sctpnat] a number of problems may arise as it tries
to communicate with its peer:
o More than one server behind a NAT may pick the same VTag and
source port when talking to the same peer server. This creates a source 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 5 associations apart. This situation is discussed in Section 6.
o When an SCTP endpoint is a server and talking with multiple peers o When an SCTP endpoint is a server and talking with multiple peers
and the peers are behind the same NAT, to the server the two and the peers are behind the same NAT, to the server the two
endpoints cannot be distinguished. This case is discussed in endpoints cannot be distinguished. This case is discussed in
Section 6.2. Section 7.
o A NAT could at one point during a conversation restart causing all o A NAT could at one point during a conversation restart causing all
of its state to be lost. This problem and its solution is of its state to be lost. This problem and its solution is
discussed in Section 6. discussed in Section 8.
o An SCTP endpoint may be behind two NAT's giving it redundancy. o An SCTP endpoint may be behind two NAT's giving it redundancy.
The method to set up this scenario is discussed in Section 6.1. The method to set up this scenario is discussed in Section 9.
Each of these solutions requires additional chunks and parameters, Each of these solutions 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]. from those specified in [RFC4960].
5. Handling of internal port number and verification tag collisions 5. Association Setup Considerations
Every association MUST initially be set up single-homed. There MUST
NOT be any IPv4 Address parameter, IPv6 Address parameter, or
Supported Address Types parameter in the INIT-chunk. The INIT-ACK
chunk MUST NOT contain any IPv4 Address parameter or IPv6 Address
parameter.
If the association should finally be multi-homed, the procedure in
Section 9 MUST be used.
The INIT and INIT-ACK chunk SHOULD contain the Disable Restart
parameter defined in Section 7.
6. 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
incoming packets anymore. But this is very unlikely. The Internal- incoming packets anymore. But this is very unlikely. The Internal-
VTags are chosen at random and if the Internal-Ports are also chosen VTags are chosen at random and if the Internal-Ports are also chosen
from the ephemeral port range at random this gives a 46 bit random from the ephemeral port range at random this gives a 46-bit random
number which has to match. In the TCP like NAPT case the NAT box can number which has to match. In the TCP like NAPT case the NAT box can
control the 16 bit Natted Port. control the 16-bit Natted Port.
The same can happen when the INIT-ACK is processed by the NAT.
However, in this unlikely event the NAT box MUST respond to the INIT However, in this unlikely event the NAT box MUST respond to the INIT
chunk by sending an ABORT chunk with the M-bit set. The M-bit is a chunk by sending an ABORT chunk with the M-bit set. The M-bit is a
new bit defined by this document to express to SCTP that the source new bit defined by this document to express to SCTP that the source
of this packet is a "middle" box, not the peer SCTP endpoint. The of this packet is a "middle" box, not the peer SCTP endpoint. The
source address of the packet containing the ABORT chunk MUST be the source address of the packet containing the ABORT chunk MUST be the
destination address of the SCTP packet containing the INIT chunk. destination address of the SCTP packet containing the INIT chunk.
The sender of the packet containing the INIT chunk, upon reception of The sender of the packet containing the INIT chunk, upon reception of
an ABORT with M-bit set SHOULD reinitiate the association setup an ABORT with M-bit set SHOULD reinitiate the association setup
procedure after choosing a new initiate tag. These proceedures procedure after choosing a new initiate tag. These procedures SHOULD
SHOULD be followed only if the appropriate error cause code for be followed only if the appropriate error cause code for colliding
colliding NAT table state is included AND the association is in the NAT table state is included AND the association is in the COOKIE-WAIT
COOKIE-WAIT state (i.e. it is awaiting a INIT-ACK). If the endpoint state (i.e. it is awaiting a INIT-ACK). If the endpoint is in any
is in any other state an SCTP endpoint SHOULD NOT respond. other state an SCTP endpoint SHOULD NOT respond.
The ABORT chunk defined in [RFC4960] is therefore extended by using The ABORT chunk defined in [RFC4960] is therefore extended by using
the following format: the following format:
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 following error cause with cause code 0x00B0 (Colliding NAT table Extended ABORT chunk
entry) MUST be included in the ABORT chunk:
0 1 2 3 The following error cause with cause code 0x00B0 (V-tag and Port
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 Number Collision) MUST be included in the ABORT chunk:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=0x00B0 | Cause Length=Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ INIT chunk /
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6. Handling of missing state 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 = 0x00B0 | Cause Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ INIT chunk /
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If the NAT box receives a packet for which the lookup procedure does V-tag and Port Number Collision error cause
not find an entry in the NAT table, a packet containing an ERROR
packet is sent back with the M-bit set. The source address of the FIXME: What to do when this is collision happens when processing an
packet containing the ERROR chunk MUST be the destination address of ASCONF chunk?
the incoming SCTP packet. The verification tag is reflected.
7. Handling of Internal Port Number Collisions
When two SCTP hosts are behind a NAT and using the recommendations in
[I-D.ietf-behave-sctpnat] it is possible that 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 Internet. For the
NAT appropriate tracking may be performed by assuring that the VTags
are unique between the two hosts as defined in
[I-D.ietf-behave-sctpnat]. 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 have chosen the same Internal-Port the
server cannot distinguish both associations based on the address and
port numbers. For the server it looks like the association is being
restarted. To overcome this limitation the client sends a Disable
Restart parameter in the INIT-chunk which is defined as follows:
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 = 0xC007 | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Disable Restart parameter
When the server receives this parameter it MUST do the following:
o Include in the INIT-ACK a Disable Restart parameter to inform the
client that it will support the feature.
o Disable the restart procedures defined in [RFC4960] for this
association.
Servers that support this feature will need to be capable of
maintaining multiple connections to what appears to be the same peer
(behind the NAT) differentiated only by the VTags.
The NAT, when processing the INIT-ACK, should note in its internal
table that the association supports the Disable Restart extension.
This note is used when establishing future associations (i.e. when
processing an INIT from an internal host) to decide if the connection
should be allowed. The NAT MUST do the following when processing an
INIT:
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
internal mapping table.
o If the INIT matches the external address and port of an already
existing connection, validate that the external server supports
the Disable Restart feature. If it does allow the INIT to be
forwarded.
o If the external server does not support the Disable Restart
extension the NAT MUST send an ABORT with the M-bit set.
The following error cause with cause code 0x00B2 (Port Number
Collision) MUST be included in the ABORT chunk:
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 = 0x00B2 | Cause Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ INIT chunk /
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Port Number Collision error cause
8. Handling of Missing State
If the NAT box receives a packet from the internal network for which
the lookup procedure does not find an entry in the NAT table, a
packet containing an ERROR chunk is sent back with the M-bit set.
The source address of the packet containing the ERROR chunk MUST be
the destination address of the incoming SCTP packet. The
verification tag is reflected and the T-bit is set. Please note that
such an packet containing an ERROR chunk SHOULD NOT be sent if the
received packet contains an ABORT, SHUTDOWN-COMPLETE or INIT-ACK
chunk.
The ERROR chunk defined in [RFC4960] is therefore extended by using The ERROR chunk defined in [RFC4960] is therefore extended by using
the following format: the following format:
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 following error cause with cause code 0x00B1 (Missing NAT table Extended ERROR chunk
entry) SHOULD be included in the ERROR chunk:
0 1 2 3 The following error cause with cause code 0x00B1 (Missing State)
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 SHOULD be included in the ERROR chunk:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=0x00B1 | Cause Length=Variable | 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
\ Incoming Packet / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ \ | Cause Code = 0x00B1 | Cause Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ Incoming Packet /
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Missing State error cause
Upon reception by an SCTP end-point with this ERROR chunk the Upon reception by an SCTP end-point with this ERROR chunk the
receiver SHOULD take the following actions: receiver SHOULD take the following actions:
o Validate the verifcation tag is reflected by looking at the V-tag o Validate the verification tag is reflected by looking at the VTag
that would have been included in the outgoing packet. that would have been included in the outgoing packet.
o Validate that the peer of the SCTP assocation supports the dynamic o Validate that the peer of the SCTP association supports the
address extension, if it does not discard the incoming ERROR dynamic address extension, if it does not discard the incoming
chunk. ERROR chunk.
o Generate a new ASCONF chunk as defined below including both sets o Generate a new ASCONF chunk containing the V-tags parameter as
of V-tags so that the NAT may recover the appropriate state. The defined in Figure 2 and the Disable Restart parameter if the
procedures for generating an ASCONF can be found in [RFC5061] association is using the disabled restart feature. By processing
this packet the NAT can recover the appropriate state. The
procedures for generating an ASCONF chunk can be found in
[RFC5061].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter Type = 0xC008 | Parameter Length = 16 | | Parameter Type = 0xC008 | Parameter Length = 16 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASCONF-Request Correlation ID | | ASCONF-Request Correlation ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Internal Verification Tag | | Internal Verification Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Verification Tag | | External Verification Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: V-tags parameter
If the NAT box receives a packet for which it has no NAT table entry If the NAT box receives a packet for which it has no NAT table entry
and the packet contains an ASCONF chunk with a vtag parameter, the and the packet contains an ASCONF chunk with the V-tags parameter,
NAT box MUST update its NAT table according to the verification tags the NAT box MUST update its NAT table according to the verification
in the vtag parameter. tags in the V-tags parameter and the optional Disable Restart
parameter.
The peer SCTP endpoint receiving such an ASCONF chunk SHOULD either The peer SCTP endpoint receiving such an ASCONF chunk SHOULD either
add the address and respond with an acknowledgment, if the address is add the address and respond with an acknowledgment, if the address is
new to the assocation (following all procedures defined in new to the association (following all procedures defined in
[RFC5061]). Or, if the address is already part of the association, [RFC5061]). Or, if the address is already part of the association,
the SCTP endpoint MUST NOT respond with an error, but instead should the SCTP endpoint MUST NOT respond with an error, but instead should
respond with an ASCONF-ACK acknowledging the address but take no respond with an ASCONF-ACK chunk acknowledging the address but take
action (since the address is already in the association). no action (since the address is already in the association).
6.1. Multi Point Traversal considerations 9. Multi Point Traversal Considerations
If a multi-homed SCTP end-point behind a NAT connects to a peer, it If a multi-homed SCTP end-point 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
adds 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 vtag parameter pair illustrated address SHOULD also contain the V-tags parameter and optionally the
above. Disable Restart parameter as illustrated above.
6.2. Handling of internal port number collisions 10. Socket API Considerations
When two SCTP hosts are behind a NAT and using the recommendations in This section describes how the socket API defined in [RFC6458] is
xxxxbehavexxx it is possible that two SCTP hosts in the Private- extended to provide a way for the application to control NAT
Address space will want to set up an SCTP association with the same friendliness.
server running on the same host in the Internet. For the NAT
appropriate tracking may be performed by assuring that the vtags are
unique between the two hosts as defined in xxxxbehavexxx. 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
have chosen the same Internal-Port the server cannot distinguish both
associations based on the address and port numbers. For the server
it looks like the association is being restarted. To overcome this
limitation the client sends a DISABLE_RESTART parameter in the INIT-
chunk which is defined as follows:
0 1 2 3 Please note that this section is informational only.
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 = 0xC007 | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
When the server receives this parameter it MUST do the following: A socket API implementation based on [RFC6458] is extended by
supporting one new read/write socket option.
o Include in the INIT-ACK a DISABLE_RESTART parameter to inform the 10.1. Get or Set the NAT Friendliness (SCTP_NAT_FRIENDLY)
client that it will support the feature.
o Disable the restart procdures defined in [RFC4960] for this This socket option can be used to set the NAT friendliness for future
association. associations and and retrieve the value for future and current ones.
Servers that support this feature will need to be capable of struct sctp_assoc_value {
maintaining multiple connections to what appears to be the same peer sctp_assoc_t assoc_id;
(behind the NAT) differentiated only by the vtags. uint32_t assoc_value;
};
The NAT, when processing the INIT-ACK, should note in its internal assoc_id: This parameter is ignored for one-to-one style sockets.
table that the external server supports the DISABLE_RESTART For one-to-many style sockets the application may fill in an
extension. This note is used when establishing future associations association identifier or SCTP_FUTURE_ASSOC for this query. It is
(i.e. when processing an INIT from an internal host) to decide if the an error to use SCTP_{CURRENT|ALL}_ASSOC in assoc_id.
connection should be allowed. The NAT MUST do the following when
processing an INIT:
o If the INIT is destined to an external address and port for which assoc_value: A non-zero value indicates a NAT-friendly mode.
the NAT has no outbound connection, allow the INIT creating an
internal mapping table.
o If the INIT matches the external address and port of an already 11. IANA Considerations
existing connection, validate that the external server supports
the DISABLE_RESTART feature. If it does allow the INIT to be
forwarded.
o If the external server does NOT support the DISABLE_RESTART [NOTE to RFC-Editor:
extension the NAT MUST send an ABORT with the 'M' bit set.
The following error cause with cause code 0x00B2 (Duplicate Local "RFCXXXX" is to be replaced by the RFC number you assign this
Port with DISABLE_RESTART not Supported) MUST be included in the document.
ABORT chunk:
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=0x00B2 | Cause Length=Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ INIT chunk /
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7. IANA Considerations [NOTE to RFC-Editor:
TBD The suggested values for the chunk type and the chunk parameter
types are tentative and to be confirmed by IANA.
8. Security considerations ]
TBD This document (RFCXXXX) is the reference for all registrations
described in this section. The suggested changes are described
below.
9. Acknowledgments 11.1. New Chunk Flags for Two Chunk Types
The authors wish to thank Qiaobing Xie, Henning Peters, Bryan Ford, As defined in [RFC6096] two chunk flags have to be assigned by IANA
David Hayes, Alfred Hines, Dan Wing, and Jason But for their for the ERROR chunk. The suggested value for the T bit is 0x01 and
invaluable comments. for the M bit is 0x02.
10. References This requires an update of the "ERROR Chunk Flags" registry for SCTP:
10.1. Normative References ERROR Chunk Flags
Chunk Flag Value Chunk Flag Name Reference
0x01 T bit [RFCXXXX]
0x02 M Bit [RFCXXXX]
0x04 Unassigned
0x08 Unassigned
0x10 Unassigned
0x20 Unassigned
0x40 Unassigned
0x80 Unassigned
As defined in [RFC6096] one chunk flag has to be assigned by IANA for
the ABORT chunk. The suggested value of the M bit is 0x02.
This requires an update of the "ABORT Chunk Flags" registry for SCTP:
ABORT Chunk Flags
Chunk Flag Value Chunk Flag Name Reference
0x01 T bit [RFC4960]
0x02 M Bit [RFCXXXX]
0x04 Unassigned
0x08 Unassigned
0x10 Unassigned
0x20 Unassigned
0x40 Unassigned
0x80 Unassigned
11.2. Three New Error Causes
Three error causes have to be assigned by IANA. It is suggested to
use the values given below.
This requires three additional lines in the "Error Cause Codes"
registry for SCTP:
Chunk Parameter Types
Value Cause Code Reference
-------- ------------------------------------------------ ---------
176 V-tag and Port Number Collision [RFCXXXX]
177 Missing State [RFCXXXX]
178 Port Number Collision [RFCXXXX]
11.3. Two New Chunk Parameter Types
Two chunk parameter types have to be assigned by IANA. It is
suggested to use the values given below. IANA should assign these
values from the pool of parameters with the upper two bits set to
'11'.
This requires two additional lines in the "Chunk Parameter Types"
registry for SCTP:
Chunk Parameter Types
ID Value Chunk Parameter Type Reference
-------- ------------------------------------------------ ---------
49159 Disable Restart (0xC007) [RFCXXXX]
49160 V-tags (0xC008) [RFCXXXX]
12. Security Considerations
The document does not add any additional security considerations to
the ones given in [RFC4960], [RFC4895], and [RFC5061].
13. Acknowledgments
The authors wish to thank Jason But, Bryan Ford, David Hayes, Alfred
Hines, Henning Peters, Timo Voelker, Dan Wing, and Qiaobing Xie for
their invaluable comments.
14. References
14.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981. RFC 793, September 1981.
[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,
"Authenticated Chunks for the Stream Control Transmission
Protocol (SCTP)", RFC 4895, August 2007.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol", [RFC4960] Stewart, R., "Stream Control Transmission Protocol",
RFC 4960, September 2007. RFC 4960, September 2007.
[RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M. [RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
Kozuka, "Stream Control Transmission Protocol (SCTP) Kozuka, "Stream Control Transmission Protocol (SCTP)
Dynamic Address Reconfiguration", RFC 5061, Dynamic Address Reconfiguration", RFC 5061,
September 2007. September 2007.
10.2. Informative References [RFC6096] Tuexen, M. and R. Stewart, "Stream Control Transmission
Protocol (SCTP) Chunk Flags Registration", RFC 6096,
January 2011.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and 14.2. Informative References
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996. [RFC5735] Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses",
BCP 153, RFC 5735, January 2010.
[RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V.
Yasevich, "Sockets API Extensions for the Stream Control
Transmission Protocol (SCTP)", RFC 6458, December 2011.
[I-D.ietf-behave-sctpnat]
Stewart, R., Tuexen, M., and I. Ruengeler, "Stream Control
Transmission Protocol (SCTP) Network Address Translation",
draft-ietf-behave-sctpnat-06 (work in progress),
March 2012.
Authors' Addresses Authors' Addresses
Randall R. Stewart Randall R. Stewart
Adara Networks Adara Networks
Chapin, SC 29036 Chapin, SC 29036
USA US
Phone:
Email: randall@lakerest.net Email: randall@lakerest.net
Michael Tuexen Michael Tuexen
Muenster Univ. of Applied Sciences Muenster University of Applied Sciences
Stegerwaldstr. 39 Stegerwaldstrasse 39
48565 Steinfurt 48565 Steinfurt
Germany DE
Email: tuexen@fh-muenster.de Email: tuexen@fh-muenster.de
Irene Ruengeler Irene Ruengeler
Muenster Univ. of Applied Sciences Muenster University of Applied Sciences
Stegerwaldstr. 39 Stegerwaldstrasse 39
48565 Steinfurt 48565 Steinfurt
Germany DE
Email: i.ruengeler@fh-muenster.de Email: i.ruengeler@fh-muenster.de
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