draft-ietf-tsvwg-natsupp-03.txt   draft-ietf-tsvwg-natsupp-04.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: April 12, 2013 I. Ruengeler Expires: April 24, 2013 I. Ruengeler
Muenster Univ. of Appl. Sciences Muenster Univ. of Appl. Sciences
October 9, 2012 October 21, 2012
Stream Control Transmission Protocol (SCTP) Network Address Translation Stream Control Transmission Protocol (SCTP) Network Address Translation
for Endpoints Support
draft-ietf-tsvwg-natsupp-03.txt draft-ietf-tsvwg-natsupp-04.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
skipping to change at page 1, line 48 skipping to change at page 1, line 48
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 April 12, 2013. This Internet-Draft will expire on April 24, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 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
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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Problem Space Overview . . . . . . . . . . . . . . . . . . . . 5 4. Data Formats . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Handling of Internal Port Number and Verification Tag 4.1. Modified Chunks . . . . . . . . . . . . . . . . . . . . . 6
Collisions . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1.1. Extended ABORT Chunk . . . . . . . . . . . . . . . . . 6
6. Handling of Missing State . . . . . . . . . . . . . . . . . . 7 4.1.2. Extended ERROR Chunk . . . . . . . . . . . . . . . . . 7
7. Multi Point Traversal Considerations . . . . . . . . . . . . . 8 4.2. New Error Causes . . . . . . . . . . . . . . . . . . . . . 7
8. Handling of Internal Port Number Collisions . . . . . . . . . 8 4.2.1. V-Tag and Port Number Collision Error Cause . . . . . 7
9. SCTP Socket API Considerations . . . . . . . . . . . . . . . . 10 4.2.2. Missing State Error Cause . . . . . . . . . . . . . . 8
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 4.2.3. Port Number Collision Error Cause . . . . . . . . . . 8
11. Security Considerations . . . . . . . . . . . . . . . . . . . 10 4.3. New Parameters . . . . . . . . . . . . . . . . . . . . . . 9
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 4.3.1. Disable Restart Parameter . . . . . . . . . . . . . . 9
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.3.2. V-Tags Parameter . . . . . . . . . . . . . . . . . . . 9
13.1. Normative References . . . . . . . . . . . . . . . . . . 10 5. Problem Space and Procedures . . . . . . . . . . . . . . . . . 11
13.2. Informative References . . . . . . . . . . . . . . . . . 11 5.1. Problem Space Overview . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 5.2. Association Setup Considerations . . . . . . . . . . . . . 11
5.3. Handling of Internal Port Number and Verification Tag
Collisions . . . . . . . . . . . . . . . . . . . . . . . . 11
5.4. Handling of Internal Port Number Collisions . . . . . . . 12
5.5. Handling of Missing State . . . . . . . . . . . . . . . . 13
5.6. Multi Point Traversal Considerations . . . . . . . . . . . 15
6. Socket API Considerations . . . . . . . . . . . . . . . . . . 15
6.1. Get or Set the NAT Friendliness (SCTP_NAT_FRIENDLY) . . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7.1. New Chunk Flags for Two Chunk Types . . . . . . . . . . . 16
7.2. Three New Error Causes . . . . . . . . . . . . . . . . . . 17
7.3. Two New Chunk Parameter Types . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . . 18
10.2. Informative References . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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 (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 maintain 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 procedures for generating appropriate A NAT will need to follow these procedures for generating appropriate
SCTP packet formats. NAT's should refer to [I-D.ietf-behave-sctpnat] SCTP packet formats. NAT's should refer to [I-D.ietf-behave-sctpnat]
skipping to change at page 5, line 18 skipping to change at page 6, line 18
+---------+ 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
Figure 1: Basic network setup Figure 1: Basic network setup
4. Problem Space Overview 4. Data Formats
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
situation where the NAT will not be able to tell the two
associations apart. This situation is discussed in Section 5.
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
endpoints cannot be distinguished. This case is discussed in
Section 8.
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
discussed in Section 6.
o An SCTP endpoint may be behind two NAT's giving it redundancy.
The method to set up this scenario is discussed in Section 7.
Each of these solutions requires additional chunks and parameters, 4.1. Modified Chunks
defined in this document, and possibly modified handling procedures
from those specified in [RFC4960].
5. Handling of Internal Port Number and Verification Tag Collisions This section presents existing chunks defined in [RFC4960] that are
modified by this document.
Consider the case where two hosts in the Private-Address space want 4.1.1. Extended ABORT Chunk
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
External-Address are the same. If they both choose the same
Internal-Port and Internal-VTag, the NAT box cannot distinguish
incoming packets anymore. But this is very unlikely. The Internal-
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
number which has to match. In the TCP like NAPT case the NAT box can
control the 16-bit Natted Port.
However, in this unlikely event the NAT box MUST respond to the INIT 0 1 2 3
chunk by sending an ABORT chunk with the M-bit set. The M-bit is a 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
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 | Type = 6 | Reserved |M|T| Length |
source address of the packet containing the ABORT chunk MUST be the +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
destination address of the SCTP packet containing the INIT chunk. \ \
/ zero or more Error Causes /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The sender of the packet containing the INIT chunk, upon reception of The ABORT chunk is extended to add the new 'M-bit'. The M-bit
an ABORT with M-bit set SHOULD reinitiate the association setup indicates to the receiver of the ABORT chunk that the chunk was not
procedure after choosing a new initiate tag. These procedures SHOULD generated by the peer SCTP endpoint, but instead by a middle box.
be followed only if the appropriate error cause code for colliding
NAT table state is included AND the association is in the COOKIE-WAIT
state (i.e. it is awaiting a INIT-ACK). If the endpoint is in any
other state an SCTP endpoint SHOULD NOT respond.
The ABORT chunk defined in [RFC4960] is therefore extended by using 4.1.2. Extended ERROR Chunk
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 = 9 | 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 The ERROR chunk defined in [RFC4960] is extended to add the new
entry) MUST be included in the ABORT chunk: '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
a middle box.
4.2. New Error Causes
This section defines the new error causes added by this document.
4.2.1. V-Tag 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ INIT chunk / \ INIT chunk /
/ \ / \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6. Handling of Missing State Cause Code: 2 bytes (unsigned integer)
This field holds the IANA defined cause code for the V-tag and
Port Number Collision Error Cause. The suggested value of this
field for IANA is 0x00B0.
If the NAT box receives a packet for which the lookup procedure does Cause Length: 2 bytes (unsigned integer)
not find an entry in the NAT table, a packet containing an ERROR This field holds the length in bytes of the error cause. The
packet is sent back with the M-bit set. The source address of the value MUST be the length of the Cause-Specific Information plus 4.
packet containing the ERROR chunk MUST be the destination address of
the incoming SCTP packet. The verification tag is reflected.
The ERROR chunk defined in [RFC4960] is therefore extended by using INIT chunk: variable length
the following format: The Cause-Specific Information is filled with the INIT chunk that
caused this error. 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 truncated.
4.2.2. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 9 | Reserved |M|T| Length | | Cause Code = 0x00B1 | Cause Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \ \ Incoming Packet /
/ zero or more Error Causes / / \
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following error cause with cause code 0x00B1 (Missing NAT table Cause Code: 2 bytes (unsigned integer)
entry) SHOULD be included in the ERROR chunk: This field holds the IANA defined cause code for the Missing State
Error Cause. The suggested value of this field for IANA is
0x00B1.
Cause Length: 2 bytes (unsigned integer)
This field holds the length in bytes of the error cause. The
value MUST be the length of the Cause-Specific Information plus 4.
Incoming Packet: variable length
The Cause-Specific Information is filled with the IPv4 or IPv6
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
or ABORT chunk being sent then the bytes that do not fit are
truncated.
4.2.3. 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 = 0x00B1 | Cause Length = Variable | | Cause Code = 0x00B2 | Cause Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ Incoming Packet / \ INIT chunk /
/ \ / \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Upon reception by an SCTP end-point with this ERROR chunk the Cause Code: 2 bytes (unsigned integer)
receiver SHOULD take the following actions: This field holds the IANA defined cause code for the Port Number
Collision Error Cause. The suggested value of this field for IANA
is 0x00B2.
o Validate the verification tag is reflected by looking at the VTag Cause Length: 2 bytes (unsigned integer)
that would have been included in the outgoing packet. This field holds the length in bytes of the error cause. The
value MUST be the length of the Cause-Specific Information plus 4.
o Validate that the peer of the SCTP association supports the INIT chunk: variable length
dynamic address extension, if it does not discard the incoming The Cause-Specific Information is filled with the INIT chunk that
ERROR chunk. caused this error. 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 truncated.
o Generate a new ASCONF chunk as defined below including both sets 4.3. New Parameters
of VTags so that the NAT may recover the appropriate state. The
procedures for generating an ASCONF chunk can be found in This section defines new parameters and there valid appearance
[RFC5061]. defined by this document.
4.3.1. Disable Restart Parameter
This parameter is used to indicate that the RESTART procedure is
requested to be disabled. Both endpoints of an association MUST
include this parameter in the INIT chunk and INIT-ACK chunk when
establishing an association and MUST include it in the ASCONF chunk
when adding an address to successfully disable the restart procedure.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Parameter Type: 2 bytes (unsigned integer)
This field holds the IANA defined parameter type for the Disable
Restart Parameter. The suggested value of this field for IANA is
0xC007.
Parameter Length: 2 bytes (unsigned integer)
This field holds the length in bytes of the parameter. The value
MUST be 4.
This parameter MAY appear in INIT, INIT-ACK and ASCONF chunks and
MUST NOT appear in any other chunk.
4.3.2. V-Tags Parameter
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If the NAT box receives a packet for which it has no NAT table entry Parameter Type: 2 bytes (unsigned integer)
and the packet contains an ASCONF chunk with a VTAG parameter, the This field holds the IANA defined parameter type for the Disable
NAT box MUST update its NAT table according to the verification tags Restart Parameter. The suggested value of this field for IANA is
in the VTAG parameter. 0xC008.
The peer SCTP endpoint receiving such an ASCONF chunk SHOULD either Parameter Length: 2 bytes (unsigned integer)
add the address and respond with an acknowledgment, if the address is This field holds the length in bytes of the parameter. The value
new to the association (following all procedures defined in MUST be 16.
[RFC5061]). Or, if the address is already part of the association,
the SCTP endpoint MUST NOT respond with an error, but instead should
respond with an ASCONF-ACK chunk acknowledging the address but take
no action (since the address is already in the association).
7. Multi Point Traversal Considerations ASCONF-Request Correlation ID: 4 bytes (unsigned integer)
This is an opaque integer assigned by the sender to identify each
request parameter. The receiver of the ASCONF Chunk will copy
this 32-bit value into the ASCONF Response Correlation ID field of
the ASCONF-ACK response parameter. The sender of the ASCONF can
use this same value in the ASCONF-ACK to find which request the
response is for. Note that the receiver MUST NOT change this 32-
bit value.
If a multi-homed SCTP end-point behind a NAT connects to a peer, it Internal Verification Tag: 4 bytes (unsigned integer)
SHOULD first set up the association single-homed with only one The Verification Tag that the internal host has chosen for its
address causing the first NAT to populate its state. Then it SHOULD communication. The Verification Tag is a unique 32-bit tag that
add each IP address using ASCONF chunks sent via their respective must accompany any incoming SCTP packet for this association to
NATs. The address to add is the wildcard address and the lookup the Private-Address.
address SHOULD also contain the VTAG parameter pair illustrated
above.
8. Handling of Internal Port Number Collisions External Verification Tag: 4 bytes (unsigned integer) The
Verification Tag that the host holding the External-Address has
chosen for its communication. The VTag is a unique 32-bit tag
that must accompany any incoming SCTP packet for this association
to the External-Address.
This parameter MAY appear in ASCONF chunks and MUST NOT appear in any
other chunk.
5. Problem Space and Procedures
5.1. Problem Space Overview
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
situation where the NAT will not be able to tell the two
associations apart. This situation is discussed in Section 5.3.
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
endpoints cannot be distinguished. This case is discussed in
Section 5.4.
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
discussed in Section 5.5.
o An SCTP endpoint may be behind two NAT's giving it redundancy.
The method to set up this scenario is discussed in Section 5.6.
Each of these solutions requires additional chunks and parameters,
defined in this document, and possibly modified handling procedures
from those specified in [RFC4960].
5.2. 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 5.6 MUST be used.
The INIT and INIT-ACK chunk SHOULD contain the Disable Restart
parameter defined in Section 4.3.1.
5.3. Handling of Internal Port Number and Verification Tag Collisions
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
same host in the Internet. This means that the External-Port and the
External-Address are the same. If they both choose the same
Internal-Port and Internal-VTag, the NAT box cannot distinguish
incoming packets anymore. But this is very unlikely. The Internal-
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
number which has to match. In the TCP like NAPT case the NAT box can
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
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
of this packet is a "middle" box, not the peer SCTP endpoint (see
Section 4.1.1). The source address of the packet containing the
ABORT chunk MUST be the destination address of the SCTP packet
containing the INIT chunk.
The sender of the packet containing the INIT chunk, upon reception of
an ABORT with M-bit set SHOULD reinitiate the association setup
procedure after choosing a new initiate tag. These procedures SHOULD
be followed only if the appropriate error cause code for colliding
NAT table state is included AND the association is in the COOKIE-WAIT
state (i.e. it is awaiting a INIT-ACK). If the endpoint is in any
other state an SCTP endpoint SHOULD NOT respond.
The error cause with cause code 'V-tag and Port Number Collision'
(see Section 4.2.1) MUST be included in the ABORT chunk by the sender
of the ABORT chunk.
5.4. Handling of Internal Port Number Collisions
When two SCTP hosts are behind a NAT and using the recommendations in 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 [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 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 the same server running on the same host in the Internet. For the
NAT appropriate tracking may be performed by assuring that the VTags NAT appropriate tracking may be performed by assuring that the VTags
are unique between the two hosts as defined in are unique between the two hosts as defined in
[I-D.ietf-behave-sctpnat]. But for the external SCTP server on the [I-D.ietf-behave-sctpnat]. But for the external SCTP server on the
internet this means that the External-Port and the External-Address internet this means that the External-Port and the External-Address
are the same. If they both have chosen the same Internal-Port the are the same. If they both have chosen the same Internal-Port the
server cannot distinguish both associations based on the address and server cannot distinguish both associations based on the address and
port numbers. For the server it looks like the association is being port numbers. For the server it looks like the association is being
restarted. To overcome this limitation the client sends a restarted. To overcome this limitation the client sends a Disable
DISABLE_RESTART parameter in the INIT-chunk which is defined as Restart parameter in the INIT-chunk.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
When the server receives this parameter it MUST do the following: When the server receives this parameter it MUST do the following:
o Include in the INIT-ACK a DISABLE_RESTART parameter to inform the o Include in the INIT-ACK a Disable Restart parameter to inform the
client that it will support the feature. client that it will support the feature.
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 external server supports the DISABLE_RESTART table that the association supports the Disable Restart extension.
extension. This note is used when establishing future associations This note is used when establishing future associations (i.e. when
(i.e. when processing an INIT from an internal host) to decide if the processing an INIT from an internal host) to decide if the connection
connection should be allowed. The NAT MUST do the following when should be allowed. The NAT MUST do the following when processing an
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
the DISABLE_RESTART feature. If it does allow the INIT to be the Disable Restart feature. If it does allow the INIT to be
forwarded. forwarded.
o If the external server does not support the DISABLE_RESTART o If the external server does not support the Disable Restart
extension the NAT MUST send an ABORT with the M-bit set. extension the NAT MUST send an ABORT with the M-bit set.
The following error cause with cause code 0x00B2 (Duplicate Local The Port Number Collision error cause (see Section 4.2.3) MUST be
Port with DISABLE_RESTART not Supported) MUST be included in the included in the ABORT chunk.
ABORT chunk:
0 1 2 3 5.5. Handling of 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code = 0x00B2 | Cause Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ INIT chunk /
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
9. SCTP Socket API Considerations 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 a packet containing an ERROR chunk SHOULD NOT be sent if the
received packet contains an ABORT, SHUTDOWN-COMPLETE or INIT-ACK
chunk. An ERROR chunk MUST NOT be sent if the received packet
contains an ERROR chunk with the M-bit set.
TBD When sending the ERROR chunk, the new error cause Missing state (see
Section 4.2.2) MUST be included and the new M-bit of the ERROR chunk
MUST be set (see Section 4.1.2).
10. IANA Considerations Upon reception by an SCTP end-point with this ERROR chunk the
receiver SHOULD take the following actions:
M-Bit for ABORT and ERROR chunk (0x02). o Validate the verification tag is reflected by looking at the VTag
that would have been included in the outgoing packet.
Error cause Colliding NAT table entry, (0x00B1). o Validate that the peer of the SCTP association supports the
dynamic address extension, if it does not discard the incoming
ERROR chunk.
Error cause Duplicate Local Port with DISABLE_RESTART not Supported, o Generate a new ASCONF chunk containing the V-tags parameter (see
(0x00B2). Section 4.3.2) and the Disable Restart parameter if the
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].
Disable restart parameter (0xC007). If the NAT box receives a packet for which it has no NAT table entry
and the packet contains an ASCONF chunk with the V-tags parameter,
the NAT box MUST update its NAT table according to the verification
tags in the V-tags parameter and the optional Disable Restart
parameter.
ASCONF Parameter (0xC008). The peer SCTP endpoint receiving such an ASCONF chunk SHOULD either
add the address and respond with an acknowledgment, if the address is
new to the association (following all procedures defined in
[RFC5061]). Or, if the address is already part of the association,
the SCTP endpoint MUST NOT respond with an error, but instead should
respond with an ASCONF-ACK chunk acknowledging the address but take
no action (since the address is already in the association).
11. Security Considerations Note that it is possible that upon receiving an ASCONF chunk
containing the V-tags parameter that the NAT will realize that it has
an 'Internal Port Number and Verification Tag collision'. In such a
case the NAT MUST send an ERROR chunk with the error cause code set
to 'V-tag and Port Number Collision' (see Section 4.2.1).
TBD If an SCTP endpoint receives an ERROR with 'Internal Port Number and
Verification Tag collision' as the error cause and the packet in the
Error Chunk contains an ASCONF with the V-tag parameter, careful
examination of the association is required. The endpoint MUST do the
following:
12. Acknowledgments o Validate the verification tag is reflected by looking at the VTag
that would have been included in the outgoing packet.
o Validate that the peer of the SCTP association supports the
dynamic address extension, if it does not discard the incoming
ERROR chunk.
o If the association is attempting to add an address (i.e. following
the procedures in Section 5.6) then the endpoint MUST-NOT consider
the address part of the association and SHOULD make no further
attempt to add the address (i.e. cancel any ASCONF timers and
remove any record of the path), since the NAT has a vtag collision
and the association cannot easily create a new vtag (as it would
if the error occurred when sending an INIT).
o If the endpoint has no other path, i.e. the procedure was executed
due to missing state in the NAT, then the endpoint MUST abort the
association. This would occur only if the local NAT restarted and
accepted a new association before attempting to repair the missing
state (Note that this is no different then what happens to all TCP
connections when a NAT looses its state).
5.6. Multi Point Traversal Considerations
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
address causing the first NAT to populate its state. Then it SHOULD
add each IP address using ASCONF chunks sent via their respective
NATs. The address to add is the wildcard address and the lookup
address SHOULD also contain the V-tags parameter and optionally the
Disable Restart parameter as illustrated above.
6. Socket API Considerations
This section describes how the socket API defined in [RFC6458] is
extended to provide a way for the application to control NAT
friendliness.
Please note that this section is informational only.
A socket API implementation based on [RFC6458] is extended by
supporting one new read/write socket option.
6.1. Get or Set the NAT Friendliness (SCTP_NAT_FRIENDLY)
This socket option uses the option_level IPPROTO_SCTP and the
option_name SCTP_NAT_FRIENDLY. It can be used to enable/disable the
NAT friendliness for future associations and retrieve the value for
future and specific ones.
struct sctp_assoc_value {
sctp_assoc_t assoc_id;
uint32_t assoc_value;
};
assoc_id: This parameter is ignored for one-to-one style sockets.
For one-to-many style sockets the application may fill in an
association identifier or SCTP_FUTURE_ASSOC for this query. It is
an error to use SCTP_{CURRENT|ALL}_ASSOC in assoc_id.
assoc_value: A non-zero value indicates a NAT-friendly mode.
7. IANA Considerations
[NOTE to RFC-Editor:
"RFCXXXX" is to be replaced by the RFC number you assign this
document.
]
[NOTE to RFC-Editor:
The suggested values for the chunk type and the chunk parameter
types are tentative and to be confirmed by IANA.
]
This document (RFCXXXX) is the reference for all registrations
described in this section. The suggested changes are described
below.
7.1. New Chunk Flags for Two Chunk Types
As defined in [RFC6096] two chunk flags have to be assigned by IANA
for the ERROR chunk. The suggested value for the T bit is 0x01 and
for the M bit is 0x02.
This requires an update of the "ERROR Chunk Flags" registry for SCTP:
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
7.2. 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]
7.3. 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]
8. Security Considerations
The document does not add any additional security considerations to
the ones given in [RFC4960], [RFC4895], and [RFC5061].
9. Acknowledgments
The authors wish to thank Jason But, Bryan Ford, David Hayes, Alfred The authors wish to thank Jason But, Bryan Ford, David Hayes, Alfred
Hines, Henning Peters, Timo Voelker, Dan Wing, and Qiaobing Xie for Hines, Henning Peters, Timo Voelker, Dan Wing, and Qiaobing Xie for
their invaluable comments. their invaluable comments.
13. References 10. References
13.1. Normative References 10.1. 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, [RFC4895] Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
"Authenticated Chunks for the Stream Control Transmission "Authenticated Chunks for the Stream Control Transmission
Protocol (SCTP)", RFC 4895, August 2007. Protocol (SCTP)", RFC 4895, August 2007.
skipping to change at page 11, line 24 skipping to change at page 19, line 14
[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.
[RFC6096] Tuexen, M. and R. Stewart, "Stream Control Transmission [RFC6096] Tuexen, M. and R. Stewart, "Stream Control Transmission
Protocol (SCTP) Chunk Flags Registration", RFC 6096, Protocol (SCTP) Chunk Flags Registration", RFC 6096,
January 2011. January 2011.
[I-D.ietf-tsvwg-sctp-udp-encaps] 10.2. Informative References
Tuexen, M. and R. Stewart, "UDP Encapsulation of SCTP
Packets", draft-ietf-tsvwg-sctp-udp-encaps-04 (work in
progress), July 2012.
13.2. Informative References
[RFC5735] Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses", [RFC5735] Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses",
BCP 153, RFC 5735, January 2010. BCP 153, RFC 5735, January 2010.
[RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram
Transport Layer Security (DTLS) for Stream Control
Transmission Protocol (SCTP)", RFC 6083, January 2011.
[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.
[I-D.ietf-behave-sctpnat] [I-D.ietf-behave-sctpnat]
Stewart, R., Tuexen, M., and I. Ruengeler, "Stream Control Stewart, R., Tuexen, M., and I. Ruengeler, "Stream Control
Transmission Protocol (SCTP) Network Address Translation", Transmission Protocol (SCTP) Network Address Translation",
draft-ietf-behave-sctpnat-06 (work in progress), draft-ietf-behave-sctpnat-07 (work in progress),
March 2012. October 2012.
Authors' Addresses Authors' Addresses
Randall R. Stewart Randall R. Stewart
Adara Networks Adara Networks
Chapin, SC 29036 Chapin, SC 29036
USA US
Email: randall@lakerest.net Email: randall@lakerest.net
Michael Tuexen Michael Tuexen
Muenster University of Applied Sciences Muenster University of Applied Sciences
Stegerwaldstrasse 39 Stegerwaldstrasse 39
48565 Steinfurt 48565 Steinfurt
DE DE
Email: tuexen@fh-muenster.de Email: tuexen@fh-muenster.de
 End of changes. 56 change blocks. 
186 lines changed or deleted 491 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/