draft-ietf-tsvwg-natsupp-04.txt   draft-ietf-tsvwg-natsupp-05.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 24, 2013 I. Ruengeler Expires: August 29, 2013 I. Ruengeler
Muenster Univ. of Appl. Sciences Muenster Univ. of Appl. Sciences
October 21, 2012 February 25, 2013
Stream Control Transmission Protocol (SCTP) Network Address Translation Stream Control Transmission Protocol (SCTP) Network Address Translation
Support Support
draft-ietf-tsvwg-natsupp-04.txt draft-ietf-tsvwg-natsupp-05.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 (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 the protocol extensions required for the SCTP This document describes the protocol extensions required for the SCTP
endpoints to help NAT's provide similar features of NAPT in the endpoints to help NATs provide similar features of NAPT in the
single-point and 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 April 24, 2013. This Internet-Draft will expire on August 29, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2013 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
skipping to change at page 3, line 15 skipping to change at page 3, line 15
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Data Formats . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Data Formats . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Modified Chunks . . . . . . . . . . . . . . . . . . . . . 6 4.1. Modified Chunks . . . . . . . . . . . . . . . . . . . . . 6
4.1.1. Extended ABORT Chunk . . . . . . . . . . . . . . . . . 6 4.1.1. Extended ABORT Chunk . . . . . . . . . . . . . . . . . 6
4.1.2. Extended ERROR Chunk . . . . . . . . . . . . . . . . . 7 4.1.2. Extended ERROR Chunk . . . . . . . . . . . . . . . . . 7
4.2. New Error Causes . . . . . . . . . . . . . . . . . . . . . 7 4.2. New Error Causes . . . . . . . . . . . . . . . . . . . . . 7
4.2.1. V-Tag and Port Number Collision Error Cause . . . . . 7 4.2.1. VTag and Port Number Collision Error Cause . . . . . . 7
4.2.2. Missing State Error Cause . . . . . . . . . . . . . . 8 4.2.2. Missing State Error Cause . . . . . . . . . . . . . . 8
4.2.3. Port Number Collision Error Cause . . . . . . . . . . 8 4.2.3. Port Number Collision Error Cause . . . . . . . . . . 8
4.3. New Parameters . . . . . . . . . . . . . . . . . . . . . . 9 4.3. New Parameters . . . . . . . . . . . . . . . . . . . . . . 9
4.3.1. Disable Restart Parameter . . . . . . . . . . . . . . 9 4.3.1. Disable Restart Parameter . . . . . . . . . . . . . . 9
4.3.2. V-Tags Parameter . . . . . . . . . . . . . . . . . . . 9 4.3.2. VTags Parameter . . . . . . . . . . . . . . . . . . . 9
5. Problem Space and Procedures . . . . . . . . . . . . . . . . . 11 5. Problem Space and Procedures . . . . . . . . . . . . . . . . . 10
5.1. Problem Space Overview . . . . . . . . . . . . . . . . . . 11 5.1. Problem Space Overview . . . . . . . . . . . . . . . . . . 11
5.2. Association Setup Considerations . . . . . . . . . . . . . 11 5.2. Association Setup Considerations . . . . . . . . . . . . . 11
5.3. Handling of Internal Port Number and Verification Tag 5.3. Handling of Internal Port Number and Verification Tag
Collisions . . . . . . . . . . . . . . . . . . . . . . . . 11 Collisions . . . . . . . . . . . . . . . . . . . . . . . . 11
5.4. Handling of Internal Port Number Collisions . . . . . . . 12 5.4. Handling of Internal Port Number Collisions . . . . . . . 12
5.5. Handling of Missing State . . . . . . . . . . . . . . . . 13 5.5. Handling of Missing State . . . . . . . . . . . . . . . . 13
5.6. Multi Point Traversal Considerations . . . . . . . . . . . 15 5.6. Multi-Point Traversal Considerations . . . . . . . . . . . 15
6. Socket API Considerations . . . . . . . . . . . . . . . . . . 15 6. Socket API Considerations . . . . . . . . . . . . . . . . . . 15
6.1. Get or Set the NAT Friendliness (SCTP_NAT_FRIENDLY) . . . 15 6.1. Get or Set the NAT Friendliness (SCTP_NAT_FRIENDLY) . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7.1. New Chunk Flags for Two Chunk Types . . . . . . . . . . . 16 7.1. New Chunk Flags for Two Existing Chunk Types . . . . . . . 16
7.2. Three New Error Causes . . . . . . . . . . . . . . . . . . 17 7.2. Three New Error Causes . . . . . . . . . . . . . . . . . . 17
7.3. Two New Chunk Parameter Types . . . . . . . . . . . . . . 18 7.3. Two New Chunk Parameter Types . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18 8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1. Normative References . . . . . . . . . . . . . . . . . . . 18 10.1. Normative References . . . . . . . . . . . . . . . . . . . 19
10.2. Informative References . . . . . . . . . . . . . . . . . . 19 10.2. Informative References . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 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 using private that allows multiple hosts to reside behind a NAT using private
addresses (see [RFC5735]) and yet use only a single globally unique addresses (see [RFC5735]) 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). 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.
This document describes an SCTP specific chunks and procedures to This document describes SCTP specific packets and procedures to help
help NAT's provide similar features of NAPT in the single point and NATs provide similar features of NAPT in the single-point and multi-
multi-point traversal scenario. An SCTP implementation supporting point traversal scenario. An SCTP implementation supporting this
this extension will follow these procedures to assure that in both extension will follow these procedures to assure that in both single-
single homed and multi-homed cases a NAT will maintain the proper homed and multi-homed cases a NAT will maintain the proper state
state without needing to change port numbers. 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. NATs should refer to [I-D.ietf-behave-sctpnat]
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 |
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| Support | No Support | No Support | None | | Support | No Support | No Support | None |
| 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 for the most part the extension no communication can occur. This is because for the most
current situation i.e. SCTP packets sent externally from behind a part of the current situation i. e. SCTP packets sent externally
NAT are discarded by the NAT. In some cases, where the NAT supports from behind a NAT are discarded by the NAT. In some cases, where the
the feature but one of the two external hosts does not support the NAT supports the feature but one of the two external hosts does not
feature communication may occur but in a limited way. For example support the feature, communication may occur but in a limited way.
only one host may be able to have a connection when a collision case For example only one host may be able to have a connection when a
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
skipping to change at page 7, line 26 skipping to change at page 7, line 26
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.
4.2. New Error Causes 4.2. 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.
4.2.1. V-Tag and Port Number Collision Error Cause 4.2.1. 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ INIT chunk / \ Chunk /
/ \ / \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Cause Code: 2 bytes (unsigned integer) Cause Code: 2 bytes (unsigned integer)
This field holds the IANA defined cause code for the V-tag and This field holds the IANA defined cause code for the VTag and Port
Port Number Collision Error Cause. The suggested value of this Number Collision Error Cause. The suggested value of this field
field for IANA is 0x00B0. for IANA is 0x00B0.
Cause Length: 2 bytes (unsigned integer) Cause Length: 2 bytes (unsigned integer)
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.
INIT chunk: variable length Chunk: variable length
The Cause-Specific Information is filled with the INIT chunk that The Cause-Specific Information is filled with the chunk that
caused this error. Note that if the entire chunk will not fit in caused this error. This can be an INIT, INIT-ACK, or ASCONF
the ERROR chunk or ABORT chunk being sent then the bytes that do chunk. Note that if the entire chunk will not fit in the ERROR
not fit are truncated. chunk or ABORT chunk being sent then the bytes that do not fit are
truncated.
4.2.2. Missing State Error Cause 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code = 0x00B1 | Cause Length = Variable | | Cause Code = 0x00B1 | Cause Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ Incoming Packet / \ Incoming Packet /
/ \ / \
skipping to change at page 8, line 39 skipping to change at page 8, line 39
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.
4.2.3. Port Number Collision Error Cause 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 = 0x00B2 | Cause Length = Variable | | Cause Code = 0x00B2 | Cause Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ INIT chunk / \ chunk /
/ \ / \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Cause Code: 2 bytes (unsigned integer) Cause Code: 2 bytes (unsigned integer)
This field holds the IANA defined cause code for the Port Number This field holds the IANA defined cause code for the Port Number
Collision Error Cause. The suggested value of this field for IANA Collision Error Cause. The suggested value of this field for IANA
is 0x00B2. is 0x00B2.
Cause Length: 2 bytes (unsigned integer) Cause Length: 2 bytes (unsigned integer)
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.
INIT chunk: variable length Chunk: variable length
The Cause-Specific Information is filled with the INIT chunk that The Cause-Specific Information is filled with the chunk that
caused this error. Note that if the entire chunk will not fit in caused this error. This can be an INIT, INIT-ACK, or ASCONF
the ERROR chunk or ABORT chunk being sent then the bytes that do chunk. Note that if the entire chunk will not fit in the ERROR
not fit are truncated. chunk or ABORT chunk being sent then the bytes that do not fit are
truncated.
4.3. New Parameters 4.3. New Parameters
This section defines new parameters and there valid appearance This section defines new parameters and their valid appearance
defined by this document. defined by this document.
4.3.1. Disable Restart Parameter 4.3.1. 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
establishing an association and MUST include it in the ASCONF chunk establishing an association and MUST include it in the ASCONF chunk
when adding an address to successfully disable the restart procedure. when adding an address to successfully disable the restart procedure.
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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.
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.
4.3.2. V-Tags Parameter 4.3.2. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 VTags
Restart Parameter. The suggested value of this field for IANA is Parameter. The suggested value of this field for IANA is 0xC008.
0xC008.
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 16. MUST be 16.
ASCONF-Request Correlation ID: 4 bytes (unsigned integer) ASCONF-Request Correlation ID: 4 bytes (unsigned integer)
This is an opaque integer assigned by the sender to identify each This is an opaque integer assigned by the sender to identify each
request parameter. The receiver of the ASCONF Chunk will copy request parameter. The receiver of the ASCONF Chunk will copy
this 32-bit value into the ASCONF Response Correlation ID field of this 32-bit value into the ASCONF Response Correlation ID field of
the ASCONF-ACK response parameter. The sender of the ASCONF can the ASCONF-ACK response parameter. The sender of the ASCONF can
skipping to change at page 11, line 18 skipping to change at page 11, line 15
When an SCTP endpoint is behind a NAT which supports When an SCTP endpoint is behind a NAT which supports
[I-D.ietf-behave-sctpnat] a number of problems may arise as it tries [I-D.ietf-behave-sctpnat] a number of problems may arise as it tries
to communicate with its peer: to communicate with its peer:
o More than one server behind a NAT may pick the same VTag and 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 5.3. associations apart. This situation is discussed in Section 5.3.
o When an SCTP endpoint is a server and talking with multiple peers o When an SCTP endpoint is a server communicating with multiple
and the peers are behind the same NAT, to the server the two peers and the peers are behind the same NAT, then the two
endpoints cannot be distinguished. This case is discussed in endpoints cannot be distinguished by the server. This case is
Section 5.4. discussed in Section 5.4.
o A NAT could at one point during a conversation restart causing all o A restart of a NAT during a conversation could cause a loss of its
of its state to be lost. This problem and its solution is state. This problem and its solution is discussed in Section 5.5.
discussed in Section 5.5.
o An SCTP endpoint may be behind two NAT's giving it redundancy. o An SCTP endpoint may be behind two NATs providing redundancy. The
The method to set up this scenario is discussed in Section 5.6. method to set up this scenario is discussed in Section 5.6.
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].
5.2. Association Setup Considerations 5.2. Association Setup Considerations
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
skipping to change at page 12, line 6 skipping to change at page 11, line 51
The INIT and INIT-ACK chunk SHOULD contain the Disable Restart The INIT and INIT-ACK chunk SHOULD contain the Disable Restart
parameter defined in Section 4.3.1. parameter defined in Section 4.3.1.
5.3. Handling of Internal Port Number and Verification Tag Collisions 5.3. 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
incoming packets anymore. But this is very unlikely. The Internal- between incoming packets anymore. But this is very unlikely. The
VTags are chosen at random and if the Internal-Ports are also chosen Internal-VTags are chosen at random and if the Internal-Ports are
from the ephemeral port range at random this gives a 46-bit random also chosen from the ephemeral port range at random this gives a 46-
number which has to match. In the TCP like NAPT case the NAT box can bit random number which has to match. In the TCP like NAPT case the
control the 16-bit Natted Port. NAT box can control the 16-bit Natted Port and therefor avoid
collisions deterministically.
The same can happen when the INIT-ACK is processed by the NAT. The same can happen when an INIT-ACK chunk or an ASCONF chunk 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 send an ABORT chunk
chunk by sending an ABORT chunk with the M-bit set. The M-bit is a with the M-bit set if the collision is triggered by an INIT or INIT-
new bit defined by this document to express to SCTP that the source ACK chunk or send an ERROR chunk with the M-bit set if the collision
of this packet is a "middle" box, not the peer SCTP endpoint (see is triggered by an ASCONF chunk. The M-bit is a new bit defined by
Section 4.1.1). The source address of the packet containing the this document to express to SCTP that the source of this packet is a
ABORT chunk MUST be the destination address of the SCTP packet "middle" box, not the peer SCTP endpoint (see Section 4.1.1). In a
containing the INIT chunk. packet containing an INIT-ACK chunk triggers the collision, the
corresponding packet containing the ABORT chunk MUST contain the same
source and destination address and port numbers as the packet
containing the INIT-ACK chunk. In the other two cases, the source
and destination address and port numbers MUST be swapped.
The sender of the packet containing the INIT chunk, upon reception of The sender of the packet containing the INIT chunk or the receiver of
an ABORT with M-bit set SHOULD reinitiate the association setup the INIT-ACK chunk, upon reception of an ABORT chunk with M-bit set,
procedure after choosing a new initiate tag. These procedures SHOULD SHOULD reinitiate the association setup procedure after choosing a
be followed only if the appropriate error cause code for colliding new initiate tag. These procedures SHOULD be followed only if the
NAT table state is included AND the association is in the COOKIE-WAIT appropriate error cause code for colliding NAT table state is
state (i.e. it is awaiting a INIT-ACK). If the endpoint is in any included AND the association is in the COOKIE-WAIT state (i. e. it is
other state an SCTP endpoint SHOULD NOT respond. awaiting an 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' The sender of the ASCONF chunk, upon reception of an ERROR chunk with
(see Section 4.2.1) MUST be included in the ABORT chunk by the sender M-bit set, MUST stop adding the path to the association.
of the ABORT chunk.
The sender of the ERROR or ABORT chunk MUST include the error cause
with cause code 'VTag and Port Number Collision' (see Section 4.2.1).
5.4. Handling of Internal Port Number Collisions 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 between both associations based on the
port numbers. For the server it looks like the association is being address and port numbers. For the server it looks like the
restarted. To overcome this limitation the client sends a Disable association is being restarted. To overcome this limitation the
Restart parameter in the INIT-chunk. client sends a Disable Restart parameter 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 in the INIT-ACK a Disable Restart parameter to inform the o Include a Disable Restart parameter in the INIT-ACK 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 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
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 Port Number Collision error cause (see Section 4.2.3) MUST be The 'Port Number Collision' error cause (see Section 4.2.3) MUST be
included in the ABORT chunk. included in the ABORT chunk.
If the collision is triggered by an ASCONF chunk, a packet containing
an ERROR chunk with the 'Port Number Collision' error cause MUST be
sent back.
5.5. Handling of Missing State 5.5. Handling of Missing State
If the NAT box receives a packet from the internal network for which 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 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. 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 source address of the packet containing the ERROR chunk MUST be
the destination address of the incoming SCTP packet. The the destination address of the incoming SCTP packet. The
verification tag is reflected and the T-bit is set. Please note that 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 such a packet containing an ERROR chunk SHOULD NOT be sent if the
received packet contains an ABORT, SHUTDOWN-COMPLETE or INIT-ACK received packet contains an ABORT, SHUTDOWN-COMPLETE or INIT-ACK
chunk. An ERROR chunk MUST NOT be sent if the received packet chunk. An ERROR chunk MUST NOT be sent if the received packet
contains an ERROR chunk with the M-bit set. contains an ERROR chunk with the M-bit set.
When sending the ERROR chunk, the new error cause Missing state (see 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 Section 4.2.2) MUST be included and the new M-bit of the ERROR chunk
MUST be set (see Section 4.1.2). MUST be set (see Section 4.1.2).
Upon reception by an SCTP end-point with this ERROR chunk the Upon reception of this ERROR chunk by an SCTP endpoint the receiver
receiver SHOULD take the following actions: SHOULD take the following actions:
o Validate the verification tag is reflected by looking at the VTag o Validate that the verification tag is reflected by looking at the
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 Generate a new ASCONF chunk containing the V-tags parameter (see o Generate a new ASCONF chunk containing the VTags parameter (see
Section 4.3.2) and the Disable Restart parameter if the Section 4.3.2) and the Disable Restart parameter if the
association is using the disabled restart feature. By processing association is using the disabled restart feature. By processing
this packet the NAT can recover the appropriate state. The this packet the NAT can recover the appropriate state. The
procedures for generating an ASCONF chunk can be found in procedures for generating an ASCONF chunk can be found in
[RFC5061]. [RFC5061].
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 the V-tags parameter, and the packet contains an ASCONF chunk with the VTags parameter, the
the NAT box MUST update its NAT table according to the verification NAT box MUST update its NAT table according to the verification tags
tags in the V-tags parameter and the optional Disable Restart in the VTags parameter and the optional Disable Restart parameter.
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 association (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 chunk acknowledging the address but take respond with an ASCONF-ACK chunk acknowledging the address but take
no action (since the address is already in the association). no action (since the address is already in the association).
Note that it is possible that upon receiving an ASCONF chunk Note that it is possible that upon receiving an ASCONF chunk
containing the V-tags parameter that the NAT will realize that it has containing the VTags parameter the NAT will realize that it has an
an 'Internal Port Number and Verification Tag collision'. In such a 'Internal Port Number and Verification Tag collision'. In such a
case the NAT MUST send an ERROR chunk with the error cause code set 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). to 'VTag and Port Number Collision' (see Section 4.2.1).
If an SCTP endpoint receives an ERROR with 'Internal Port Number and If an SCTP endpoint receives an ERROR with 'Internal Port Number and
Verification Tag collision' as the error cause and the packet in the Verification Tag collision' as the error cause and the packet in the
Error Chunk contains an ASCONF with the V-tag parameter, careful Error Chunk contains an ASCONF with the VTags parameter, careful
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 the verification tag is reflected by looking at the VTag o Validate that the verification tag is reflected by looking at the
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. following o If the association is attempting to add an address (i. e.
the procedures in Section 5.6) then the endpoint MUST-NOT consider following the procedures in Section 5.6) then the endpoint MUST-
the address part of the association and SHOULD make no further NOT consider the address part of the association and SHOULD make
attempt to add the address (i.e. cancel any ASCONF timers and no further attempt to add the address (i. e. cancel any ASCONF
remove any record of the path), since the NAT has a vtag collision timers and remove any record of the path), since the NAT has a
and the association cannot easily create a new vtag (as it would VTag collision and the association cannot easily create a new VTag
if the error occurred when sending an INIT). (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 o If the endpoint has no other path, i. e. the procedure was
due to missing state in the NAT, then the endpoint MUST abort the executed due to missing a state in the NAT, then the endpoint MUST
association. This would occur only if the local NAT restarted and abort the association. This would occur only if the local NAT
accepted a new association before attempting to repair the missing restarted and accepted a new association before attempting to
state (Note that this is no different then what happens to all TCP repair the missing state (Note that this is no different than what
connections when a NAT looses its state). happens to all TCP connections when a NAT looses its state).
5.6. Multi Point Traversal Considerations 5.6. Multi-Point Traversal Considerations
If a multi-homed SCTP end-point 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 V-tags 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.
6. Socket API Considerations 6. Socket API Considerations
This section describes how the socket API defined in [RFC6458] is This section describes how the socket API defined in [RFC6458] is
extended to provide a way for the application to control NAT extended to provide a way for the application to control NAT
friendliness. friendliness.
Please note that this section is informational only. Please note that this section is informational only.
skipping to change at page 16, line 37 skipping to change at page 16, line 44
The suggested values for the chunk type and the chunk parameter The suggested values for the chunk type and the chunk parameter
types are tentative and to be confirmed by IANA. types are tentative and to be confirmed by IANA.
] ]
This document (RFCXXXX) is the reference for all registrations This document (RFCXXXX) is the reference for all registrations
described in this section. The suggested changes are described described in this section. The suggested changes are described
below. below.
7.1. New Chunk Flags for Two Chunk Types 7.1. New Chunk Flags for Two Existing Chunk Types
As defined in [RFC6096] two chunk flags have to be assigned by IANA 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 ERROR chunk. The suggested value for the T bit is 0x01 and
for the M bit is 0x02. for the M bit is 0x02.
This requires an update of the "ERROR Chunk Flags" registry for SCTP: This requires an update of the "ERROR Chunk Flags" registry for SCTP:
ERROR Chunk Flags ERROR Chunk Flags
Chunk Flag Value Chunk Flag Name Reference +------------------+-----------------+-----------+
0x01 T bit [RFCXXXX] | Chunk Flag Value | Chunk Flag Name | Reference |
0x02 M Bit [RFCXXXX] +------------------+-----------------+-----------+
0x04 Unassigned | 0x01 | T bit | [RFCXXXX] |
0x08 Unassigned | 0x02 | M bit | [RFCXXXX] |
0x10 Unassigned | 0x04 | Unassigned | |
0x20 Unassigned | 0x08 | Unassigned | |
0x40 Unassigned | 0x10 | Unassigned | |
0x80 Unassigned | 0x20 | Unassigned | |
| 0x40 | Unassigned | |
| 0x80 | Unassigned | |
+------------------+-----------------+-----------+
As defined in [RFC6096] one chunk flag has to be assigned by IANA for 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. the ABORT chunk. The suggested value of the M bit is 0x02.
This requires an update of the "ABORT Chunk Flags" registry for SCTP: This requires an update of the "ABORT Chunk Flags" registry for SCTP:
ABORT Chunk Flags ABORT Chunk Flags
Chunk Flag Value Chunk Flag Name Reference +------------------+-----------------+-----------+
0x01 T bit [RFC4960] | Chunk Flag Value | Chunk Flag Name | Reference |
0x02 M Bit [RFCXXXX] +------------------+-----------------+-----------+
0x04 Unassigned | 0x01 | T bit | [RFC4960] |
0x08 Unassigned | 0x02 | M bit | [RFCXXXX] |
0x10 Unassigned | 0x04 | Unassigned | |
0x20 Unassigned | 0x08 | Unassigned | |
0x40 Unassigned | 0x10 | Unassigned | |
0x80 Unassigned | 0x20 | Unassigned | |
| 0x40 | Unassigned | |
| 0x80 | Unassigned | |
+------------------+-----------------+-----------+
7.2. Three New Error Causes 7.2. Three New Error Causes
Three error causes have to be assigned by IANA. It is suggested to Three error causes have to be assigned by IANA. It is suggested to
use the values given below. use the values given below.
This requires three additional lines in the "Error Cause Codes" This requires three additional lines in the "Error Cause Codes"
registry for SCTP: registry for SCTP:
Chunk Parameter Types Error Cause Codes
Value Cause Code Reference +-------+--------------------------------+-----------+
-------- ------------------------------------------------ --------- | Value | Cause Code | Reference |
176 V-tag and Port Number Collision [RFCXXXX] +-------+--------------------------------+-----------+
177 Missing State [RFCXXXX] | 176 | VTag and Port Number Collision | [RFCXXXX] |
178 Port Number Collision [RFCXXXX] | 177 | Missing State | [RFCXXXX] |
| 178 | Port Number Collision | [RFCXXXX] |
+-------+--------------------------------+-----------+
7.3. Two New Chunk Parameter Types 7.3. Two New Chunk Parameter Types
Two chunk parameter types have to be assigned by IANA. It is Two chunk parameter types have to be assigned by IANA. It is
suggested to use the values given below. IANA should assign these suggested to use the values given below. IANA should assign these
values from the pool of parameters with the upper two bits set to values from the pool of parameters with the upper two bits set to
'11'. '11'.
This requires two additional lines in the "Chunk Parameter Types" This requires two additional lines in the "Chunk Parameter Types"
registry for SCTP: registry for SCTP:
Chunk Parameter Types Chunk Parameter Types
ID Value Chunk Parameter Type Reference +----------+--------------------------+-----------+
-------- ------------------------------------------------ --------- | ID Value | Chunk Parameter Type | Reference |
49159 Disable Restart (0xC007) [RFCXXXX] +----------+--------------------------+-----------+
49160 V-tags (0xC008) [RFCXXXX] | 49159 | Disable Restart (0xC007) | [RFCXXXX] |
| 49160 | VTags (0xC008) | [RFCXXXX] |
+----------+--------------------------+-----------+
8. Security Considerations 8. Security Considerations
The document does not add any additional security considerations to The document does not add any additional security considerations to
the ones given in [RFC4960], [RFC4895], and [RFC5061]. the ones given in [RFC4960], [RFC4895], and [RFC5061].
9. Acknowledgments 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
 End of changes. 60 change blocks. 
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