draft-ietf-sipcore-dns-dual-stack-04.txt   draft-ietf-sipcore-dns-dual-stack-05.txt 
SIPCORE O. Johansson SIPCORE O. Johansson
Internet-Draft Edvina AB Internet-Draft Edvina AB
Updates: RFC 3263 (if approved) G. Salgueiro Updates: 3263 (if approved) G. Salgueiro
Intended status: Standards Track Cisco Systems Intended status: Standards Track Cisco Systems
Expires: August 26, 2016 V. Gurbani Expires: October 17, 2016 V. Gurbani
Bell Labs, Alcatel-Lucent Bell Labs, Alcatel-Lucent
D. Worley, Ed. D. Worley, Ed.
Ariadne Ariadne
February 23, 2016 April 15, 2016
Locating Session Initiation Protocol (SIP) Servers in a Dual-Stack IP Locating Session Initiation Protocol (SIP) Servers in a Dual-Stack IP
Network Network
draft-ietf-sipcore-dns-dual-stack-04 draft-ietf-sipcore-dns-dual-stack-05
Abstract Abstract
RFC 3263 defines how a Session Initiation Protocol (SIP) RFC 3263 defines how a Session Initiation Protocol (SIP)
implementation, given a SIP Uniform Resource Identifier (URI), should implementation, given a SIP Uniform Resource Identifier (URI), should
locate the next hop SIP server using Domain Name System (DNS) locate the next-hop SIP server using Domain Name System (DNS)
procedures. As SIP networks increasingly transition from IPv4-only procedures. As SIP networks increasingly transition from IPv4-only
to dual-stack, a quality user experience must be ensured for dual- to dual-stack, a quality user experience must be ensured for dual-
stack SIP implementations. This document updates the DNS procedures stack SIP implementations. This document updates the DNS procedures
described in RFC 3263 for dual-stack SIP implementations in described in RFC 3263 for dual-stack SIP implementations in
preparation for forthcoming specifications for applying Happy preparation for forthcoming specifications for applying Happy
Eyeballs to SIP. Eyeballs principles to SIP.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 26, 2016. This Internet-Draft will expire on October 17, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. DNS Procedures in a Dual-Stack Network . . . . . . . . . . . 4
4. DNS Procedures in a Dual-Stack Network . . . . . . . . . . . 4 3.1. Dual-Stack SIP UA DNS Record Lookup Procedure . . . . . . 4
4.1. Dual-Stack SIP UA DNS Record Lookup Procedure . . . . . . 4 3.2. Indicating Address Family Preference in DNS SRV Records . 5
4.2. Indicating Address Family Preference in DNS SRV Records . 5 4. Clarification of RFC 6157 . . . . . . . . . . . . . . . . . . 5
5. Clarification of RFC 6157 . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 8. Revision History . . . . . . . . . . . . . . . . . . . . . . 7
9. Revision History . . . . . . . . . . . . . . . . . . . . . . 6 8.1. Changes from draft-ietf-sipcore-dns-dual-stack-04 to
9.1. Changes from draft-ietf-sipcore-dns-dual-stack-03 to draft-ietf-sipcore-dns-dual-stack-05 . . . . . . . . . . 7
draft-ietf-sipcore-dns-dual-stack-04 . . . . . . . . . . 6 8.2. Changes from draft-ietf-sipcore-dns-dual-stack-03 to
9.2. Changes from draft-ietf-sipcore-dns-dual-stack-02 to draft-ietf-sipcore-dns-dual-stack-04 . . . . . . . . . . 8
draft-ietf-sipcore-dns-dual-stack-03 . . . . . . . . . . 6 8.3. Changes from draft-ietf-sipcore-dns-dual-stack-02 to
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 draft-ietf-sipcore-dns-dual-stack-03 . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
The Session Initiation Protocol (SIP, [RFC3261]) and the additional The Session Initiation Protocol (SIP, [RFC3261]) and the additional
documents that extended it provide support for both IPv4 and IPv6. documents that extended it provide support for both IPv4 and IPv6.
However, this support does not fully extend to the highly hybridized However, this support does not fully extend to the highly hybridized
environments that are characteristic of the transitional migratory environments that are characteristic of the transitional migratory
phase from IPv4 to IPv6 networks. During this phase, many server and phase from IPv4 to IPv6 networks. During this phase, many server and
client implementations run on dual-stack hosts. In such client implementations run on dual-stack hosts. In such
environments, a dual-stack host will likely suffer greater connection environments, a dual-stack host will likely suffer greater connection
delay, and by extension an inferior user experience, than an delay, and by extension an inferior user experience, than an
IPv4-only host. The need to remedy this diminished performance of IPv4-only host. The need to remedy this diminished performance of
dual-stack hosts led to the development of the Happy Eyeballs dual-stack hosts led to the development of the Happy Eyeballs
[RFC6555] algorithm, which has since been implemented in many [RFC6555] algorithm, which has since been implemented in many
protocols and applications. protocols and applications.
This document updates the DNS lookup procedures of RFC 3263[RFC3263] This document updates the DNS lookup procedures of RFC 3263 [RFC3263]
in preparation for the specification of the application of Happy in preparation for the specification of the application of Happy
Eyeballs to SIP to provide enhanced performance, and consequently Eyeballs to SIP to provide enhanced performance, and consequently
user experience, in highly hybridized dual-stack SIP networks. The user experience, in highly hybridized dual-stack SIP networks. The
procedures described herein are such that a dual-stack client should procedures described herein are such that a dual-stack client should
look up both A and AAAA records in DNS and then select the best way look up both A and AAAA records in DNS and then select the best way
to set up a network flow. The details of how the latter is done is to set up a network flow. The details of how the latter is done is
considered out of scope for this document. See the Happy Eyeballs considered out of scope for this document. See the Happy Eyeballs
algorithm and implementation and design considerations in RFC 6555 algorithm and implementation and design considerations in RFC 6555
[RFC6555] for more information about issues with setting up dual- [RFC6555] for more information about issues with setting up dual-
stack network flows. stack network flows.
This document clarifies the interaction of [RFC3263] with [RFC6157] Section 4 of this document clarifies the interaction of [RFC3263]
as described in Section 5. with [RFC6157].
2. Notational Conventions 2. Terminology
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 RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
3. Terminology
RFC 3261 [RFC3261] defines additional terms used in this document RFC 3261 [RFC3261] defines additional terms used in this document
that are specific to the SIP domain such as "proxy"; "registrar"; that are specific to the SIP domain such as "proxy", "registrar",
"redirect server"; "user agent server" or "UAS"; "user agent client" "redirect server", "user agent server" or "UAS", "user agent client"
or "UAC"; "back-to-back user agent" or "B2BUA"; "dialog"; or "UAC", "back-to-back user agent" or "B2BUA", "dialog",
"transaction"; "server transaction". "transaction", and "server transaction".
This document uses the term "SIP Server" that is defined to include This document uses the term "SIP server" that is defined to include
the following SIP entities: user agent server, registrar, redirect the following SIP entities: user agent server, registrar, redirect
server, a SIP proxy in the role of user agent server, and a B2BUA in server, a SIP proxy in the role of user agent server, and a B2BUA in
the role of a user agent server. the role of a user agent server.
This document also uses the following terminology to make clear This document also uses the following terminology to make clear
distinction between SIP entities supporting only IPv4, only IPv6 or distinction between SIP entities supporting only IPv4, only IPv6 or
supporting both IPv4 and IPv6. supporting both IPv4 and IPv6:
IPv4-only UA/UAC/UAS: An IPv4-only UA/UAC/UAS supports SIP signaling IPv4-only UA/UAC/UAS: An IPv4-only UA/UAC/UAS supports SIP signaling
and media only on the IPv4 network. It does not understand IPv6 and media only on the IPv4 network. It does not understand IPv6
addresses. addresses.
IPv6-only UA/UAC/UAS: An IPv6-only UA/UAC/UAS supports SIP signaling IPv6-only UA/UAC/UAS: An IPv6-only UA/UAC/UAS supports SIP signaling
and media only on the IPv6 network. It does not understand IPv4 and media only on the IPv6 network. It does not understand IPv4
addresses. addresses.
IPv4/IPv6 UA/UAC/UAS: A UA/UAC/UAS that supports SIP signaling and IPv4/IPv6 UA/UAC/UAS: A UA/UAC/UAS that supports SIP signaling and
media on both IPv4 and IPv6 networks; such a UA/UAC/UAS is known media on both IPv4 and IPv6 networks; such a UA/UAC/UAS is known
(and will be referred to in this document) as a "dual-stack" (and will be referred to in this document) as a "dual-stack"
[RFC4213] UA/UAC/UAS. [RFC4213] UA/UAC/UAS.
address records: The DNS records which translate a domain name into The term "address records" means the DNS records which translate a
addresses within the address family(ies) that the UA supports, as domain name into addresses within the address family(ies) that the
A RR's provide IPv4 addresses and AAAA RR's provide IPv6 entity supports (as A records provide IPv4 addresses and AAAA records
addresses. provide IPv6 addresses), regardless of whether the address family was
defined before or after this document was approved.
4. DNS Procedures in a Dual-Stack Network 3. DNS Procedures in a Dual-Stack Network
This specification introduces two normative DNS lookup procedures. This specification introduces two normative DNS lookup procedures.
These are designed to improve the performance of dual-stack clients These are designed to improve the performance of dual-stack clients
in IPv4/IPv6 networks. in IPv4/IPv6 networks.
4.1. Dual-Stack SIP UA DNS Record Lookup Procedure 3.1. Dual-Stack SIP UA DNS Record Lookup Procedure
Once the transport protocol has been determined, the procedure for Once the transport protocol has been determined, the procedure for
discovering an IP address if the TARGET is not a numeric IP address discovering an IP address if the TARGET is not a numeric IP address
but the port is explicitly stated in the URI, is detailed in but the port is explicitly stated in the URI, is detailed in
Section 4.2 of RFC 3263[RFC3263]. The piece relevant to to this Section 4.2 of RFC 3263 [RFC3263]. The piece relevant to this
discussion is: discussion is:
If the TARGET was not a numeric IP address, but a port is present If the TARGET was not a numeric IP address, but a port is present
in the URI, the client performs an A or AAAA record lookup of the in the URI, the client performs an A or AAAA record lookup of the
domain name. The result will be a list of IP addresses, each of domain name. The result will be a list of IP addresses, each of
which can be contacted at the specific port from the URI and which can be contacted at the specific port from the URI and
transport protocol determined previously. transport protocol determined previously.
Section 4.2 of RFC 3263 [RFC3263] also goes on to describe the Section 4.2 of RFC 3263 [RFC3263] also goes on to describe the
procedure for discovering an IP address if the TARGET is not a procedure for discovering an IP address if the TARGET is not a
skipping to change at page 5, line 18 skipping to change at page 5, line 16
best practice for such dual-stack networks: best practice for such dual-stack networks:
The dual-stack client SHOULD look up all address records (i.e., The dual-stack client SHOULD look up all address records (i.e.,
for all address family(ies) that it supports) for the domain name for all address family(ies) that it supports) for the domain name
and add the resulting addresses to the list of IP addresses to be and add the resulting addresses to the list of IP addresses to be
contacted. A client MUST be prepared for DNS lookups to return contacted. A client MUST be prepared for DNS lookups to return
addresses in families that it does not support; such addresses addresses in families that it does not support; such addresses
MUST be ignored as unusable and the supported addresses used as MUST be ignored as unusable and the supported addresses used as
specified herein. specified herein.
4.2. Indicating Address Family Preference in DNS SRV Records 3.2. Indicating Address Family Preference in DNS SRV Records
The Happy Eyeballs algorithm [RFC6555] is particularly effective when The Happy Eyeballs algorithm [RFC6555] is particularly effective when
dual-stack client applications have significant performance dual-stack client applications have significant performance
differences in their IPv4 or IPv6 network paths. In this common differences in their IPv4 or IPv6 network paths. In this common
scenario it is often necessary for a dual-stack client to indicate a scenario it is often necessary for a dual-stack client to indicate a
preference for either IPv4 or IPv6. A service may use DNS SRV preference for either IPv4 or IPv6. A service may use DNS SRV
records to indicate such a preference for an address family. This records to indicate such a preference for an address family. This
way, a server with a high-latency and/or low-capacity IPv4 tunnel may way, a server with a high-latency and/or low-capacity IPv4 tunnel may
indicate a preference for being contacted using IPv6. A server that indicate a preference for being contacted using IPv6. A server that
wishes to do this can use the lowest SRV priority to publish wishes to do this can use the lowest SRV priority to publish
hostnames that only resolve in IPv6 and the next priority with host hostnames that only resolve in IPv6 and the next priority with host
names that resolve in both address families. names that resolve in both address families.
5. Clarification of RFC 6157 4. Clarification of RFC 6157
[RFC6157] defers to the Source and Destination Address Selection Section 5 of [RFC6157] specifies that the addresses from the address
algorithms defined in [RFC6724] (the successor of [RFC3484]) when records for a single target DNS name for a server's DNS name must be
allowing a client to choose a specific server (c.f. Section 5 in contacted in the order specified by the Source and Destination
[RFC6157]). Address Selection algorithms defined in [RFC6724] (the successor of
[RFC3484]). Typically, this is done by using the getaddrinfo()
function to translate the target DNS name into a list of IPv4 and/or
IPv6 addresses in the order in which they are to be contacted, as
that function implements [RFC6724].
This document clarifies the process: If SRV lookup is successful, the Thus, if SRV lookup on the server's DNS name is successful, the major
major ordering of the list of destination addresses is determined by ordering of the complete list of destination addresses is determined
the priority and weight fields of the SRV records as specified in by the priority and weight fields of the SRV records (as specified in
[RFC2782]. The (minor) ordering among the destinations derived from [RFC2782]) and the (minor) ordering among the destinations derived
the "target" field of a single SRV record is determined by [RFC6724]. from the "target" field of a single SRV record is determined by
[RFC6724].
6. Security Considerations For example, consider a server with DNS name example.com, with TCP
transport specified. The relevant SRV records are:
_sip._tcp.example.com. 300 IN SRV 10 1 5060 sip-1.example.com.
_sip._tcp.example.com. 300 IN SRV 20 1 5060 sip-2.example.com.
The address records for sip-1.example.com, as ordered by [RFC6724],
are
sip-1.example.com. 300 IN AAAA 2001:0db8:58:c02::face
sip-1.example.com. 300 IN AAAA 2001:0db8:c:a06::2:cafe
sip-1.example.com. 300 IN AAAA 2001:0db8:44:204::d1ce
sip-1.example.com. 300 IN A 192.0.2.45
sip-1.example.com. 300 IN A 203.0.113.109
sip-1.example.com. 300 IN A 198.51.100.24
and the address records for sip-2.example.com, as ordered by
[RFC6724], are:
sip-2.example.com. 300 IN AAAA 2001:0db8:58:c02::dead
sip-2.example.com. 300 IN AAAA 2001:0db8:c:a06::2:beef
sip-2.example.com. 300 IN AAAA 2001:0db8:44:204::c0de
sip-2.example.com. 300 IN A 192.0.2.75
sip-2.example.com. 300 IN A 203.0.113.38
sip-2.example.com. 300 IN A 198.51.100.140
Thus, the complete list of destination addresses has this ordering:
2001:0db8:58:c02::face
2001:0db8:c:a06::2:cafe
2001:0db8:44:204::d1ce
192.0.2.45
203.0.113.109
198.51.100.24
2001:0db8:58:c02::dead
2001:0db8:c:a06::2:beef
2001:0db8:44:204::c0de
192.0.2.75
203.0.113.38
198.51.100.140
In particular, the destination addresses derived from sip-
1.example.com and those derived from sip-2.example.com are not
interleaved; [RFC6724] does not operate on the complete list. This
would be true even if the two SRV records had the same priority and
were (randomly) ordered based on their weights, as the address
records of two target DNS names are never interleaved.
5. Security Considerations
This document introduces two new normative procedures to the existing This document introduces two new normative procedures to the existing
DNS procedures used to locate SIP servers. While both of these DNS procedures used to locate SIP servers. While both of these
procedures are optimizations designed to improve the performance of procedures are optimizations designed to improve the performance of
dual-stack clients, neither introduces any new security dual-stack clients, neither introduces any new security
considerations. considerations.
The specific security vulnerabilities, attacks and threat models of The specific security vulnerabilities, attacks and threat models of
the various protocols discussed in this document (SIP, DNS, SRV the various protocols discussed in this document (SIP, DNS, SRV
records, Happy Eyeballs requirements and algorithm, etc.) are well records, Happy Eyeballs requirements and algorithm, etc.) are well
documented in their respective specifications. documented in their respective specifications.
7. IANA Considerations 6. IANA Considerations
This document does not require any actions by IANA. This document does not require any actions by IANA.
8. Acknowledgments 7. Acknowledgments
The authors would like to acknowledge the support and contribution of The authors would like to acknowledge the support and contribution of
the SIP Forum IPv6 Working Group. This document is based on a lot of the SIP Forum IPv6 Working Group. This document is based on a lot of
tests and discussions at SIPit events, organized by the SIP Forum. tests and discussions at SIPit events, organized by the SIP Forum.
This document has benefited from the expertise and review feedback of This document has benefited from the expertise and review feedback of
many participants of the IETF DISPATCH and SIPCORE WG mailing lists many participants of the IETF DISPATCH and SIPCORE WG mailing lists
as well as those on the SIP Forum IPv6 Task Group mailing list. The as well as those on the SIP Forum IPv6 Task Group mailing list. The
authors wish to specifically call out the efforts and express their authors wish to specifically call out the efforts and express their
gratitude for the detailed and thoughtful comments and corrections of gratitude for the detailed and thoughtful comments and corrections of
Dan Wing, Brett Tate, Rifaat Shekh-Yusef, Carl Klatsky, Mary Barnes, Dan Wing, Brett Tate, Rifaat Shekh-Yusef, Carl Klatsky, Mary Barnes,
Keith Drage, Cullen Jennings and Simon Perreault. Keith Drage, Cullen Jennings, Simon Perreault, Paul Kyzivat, Adam
Roach, and Richard Barnes.
The authors also thank the SIPCORE WG chairs, Paul Kyzivat and Adam
Roach, and assigned Area Director, Richard Barnes, for their support
and thorough evaluation of this work.
9. Revision History 8. Revision History
[Note to RFC Editor: Please remove this entire section upon [Note to RFC Editor: Please remove this entire section upon
publication as an RFC.] publication as an RFC.]
9.1. Changes from draft-ietf-sipcore-dns-dual-stack-03 to draft-ietf- 8.1. Changes from draft-ietf-sipcore-dns-dual-stack-04 to draft-ietf-
sipcore-dns-dual-stack-05
Simplified the acknowledgments.
Improve wording and punctuation.
Rewrote Section 4 based on critiques on the Sipcore list. Included
an example by Adam Roach.
Replaced "RR's" with "records" per suggestion by Jean Mahoney.
8.2. Changes from draft-ietf-sipcore-dns-dual-stack-03 to draft-ietf-
sipcore-dns-dual-stack-04 sipcore-dns-dual-stack-04
Changed the "updates" specification to add RFC 3263 and remove RFC Changed the "updates" specification to add RFC 3263 and remove RFC
6157. 6157.
Added Simon Perreault to the acknowledgments. Added Simon Perreault to the acknowledgments.
Minor wording changes. Minor wording changes.
9.2. Changes from draft-ietf-sipcore-dns-dual-stack-02 to draft-ietf- 8.3. Changes from draft-ietf-sipcore-dns-dual-stack-02 to draft-ietf-
sipcore-dns-dual-stack-03 sipcore-dns-dual-stack-03
Described the relationship to RFC 3263 as "update", since the Described the relationship to RFC 3263 as "update", since the
existing wording in 3263 is not what we want. Arguably, the new existing wording in 3263 is not what we want. Arguably, the new
wording is what was intended in 3263, but the existing wording either wording is what was intended in 3263, but the existing wording either
does not say that or says it in a way that is easily misunderstood. does not say that or says it in a way that is easily misunderstood.
Described the relationship to RFC 6157 as "clarification", since the Described the relationship to RFC 6157 as "clarification", since the
described interaction between 3263 and 6157 appears to be the only described interaction between 3263 and 6157 appears to be the only
reasonable interpretation. reasonable interpretation.
skipping to change at page 7, line 39 skipping to change at page 9, line 7
describes how clients look up RRs). describes how clients look up RRs).
Clarified the interaction with RFC 6157 (source and destination Clarified the interaction with RFC 6157 (source and destination
address selection in IPv6) to specify what must have been intended: address selection in IPv6) to specify what must have been intended:
The major sort of the destinations is the ordering determined by The major sort of the destinations is the ordering determined by
priority/weight in the SRV records; the addresses derived from a priority/weight in the SRV records; the addresses derived from a
single SRV record's target are minorly sorted based on RFC 6157. single SRV record's target are minorly sorted based on RFC 6157.
Removed editor's name from the acknowledgments list. Removed editor's name from the acknowledgments list.
10. References 9. References
10.1. Normative References 9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782, specifying the location of services (DNS SRV)", RFC 2782,
DOI 10.17487/RFC2782, February 2000, DOI 10.17487/RFC2782, February 2000,
<http://www.rfc-editor.org/info/rfc2782>. <http://www.rfc-editor.org/info/rfc2782>.
skipping to change at page 8, line 15 skipping to change at page 9, line 31
[RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation [RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation
Protocol (SIP): Locating SIP Servers", RFC 3263, Protocol (SIP): Locating SIP Servers", RFC 3263,
DOI 10.17487/RFC3263, June 2002, DOI 10.17487/RFC3263, June 2002,
<http://www.rfc-editor.org/info/rfc3263>. <http://www.rfc-editor.org/info/rfc3263>.
[RFC6157] Camarillo, G., El Malki, K., and V. Gurbani, "IPv6 [RFC6157] Camarillo, G., El Malki, K., and V. Gurbani, "IPv6
Transition in the Session Initiation Protocol (SIP)", Transition in the Session Initiation Protocol (SIP)",
RFC 6157, DOI 10.17487/RFC6157, April 2011, RFC 6157, DOI 10.17487/RFC6157, April 2011,
<http://www.rfc-editor.org/info/rfc6157>. <http://www.rfc-editor.org/info/rfc6157>.
10.2. Informative References 9.2. Informative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002, DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>. <http://www.rfc-editor.org/info/rfc3261>.
[RFC3484] Draves, R., "Default Address Selection for Internet [RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, Protocol version 6 (IPv6)", RFC 3484,
DOI 10.17487/RFC3484, February 2003, DOI 10.17487/RFC3484, February 2003,
 End of changes. 33 change blocks. 
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