SIPCORE O. Johansson
Internet-Draft Edvina AB
Updates: 3263 (if approved) G. Salgueiro
Intended status: Standards Track Cisco Systems
Expires: March 4, 2017 V. Gurbani
Bell Labs, Nokia Networks
D. Worley, Ed.
Ariadne
August 31, 2016
Locating Session Initiation Protocol (SIP) Servers in a Dual-Stack IP
Network
draft-ietf-sipcore-dns-dual-stack-08
Abstract
RFC 3263 defines how a Session Initiation Protocol (SIP)
implementation, given a SIP Uniform Resource Identifier (URI), should
locate the next-hop SIP server using Domain Name System (DNS)
procedures. As SIP networks increasingly transition from IPv4-only
to dual-stack, a quality user experience must be ensured for dual-
stack SIP implementations. This document updates the DNS procedures
described in RFC 3263 for dual-stack SIP implementations in
preparation for forthcoming specifications for applying Happy
Eyeballs principles to SIP.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 4, 2017.
Johansson, et al. Expires March 4, 2017 [Page 1]
Internet-Draft Locating SIP Servers in IPv4/IPv6 August 2016
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. DNS Procedures in a Dual-Stack Network . . . . . . . . . . . 4
3.1. Dual-Stack SIP UA DNS Record Lookup Procedure . . . . . . 4
3.2. Indicating Address Family Preference in DNS SRV Records . 5
4. Clarification of Interaction with RFC 6724 . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
8. Revision History . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Changes from draft-ietf-sipcore-dns-dual-stack-07 to
draft-ietf-sipcore-dns-dual-stack-08 . . . . . . . . . . 8
8.2. Changes from draft-ietf-sipcore-dns-dual-stack-06 to
draft-ietf-sipcore-dns-dual-stack-07 . . . . . . . . . . 9
8.3. Changes from draft-ietf-sipcore-dns-dual-stack-05 to
draft-ietf-sipcore-dns-dual-stack-06 . . . . . . . . . . 9
8.4. Changes from draft-ietf-sipcore-dns-dual-stack-04 to
draft-ietf-sipcore-dns-dual-stack-05 . . . . . . . . . . 9
8.5. Changes from draft-ietf-sipcore-dns-dual-stack-03 to
draft-ietf-sipcore-dns-dual-stack-04 . . . . . . . . . . 9
8.6. Changes from draft-ietf-sipcore-dns-dual-stack-02 to
draft-ietf-sipcore-dns-dual-stack-03 . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
Johansson, et al. Expires March 4, 2017 [Page 2]
Internet-Draft Locating SIP Servers in IPv4/IPv6 August 2016
1. Introduction
The Session Initiation Protocol (SIP, [RFC3261]) and the additional
documents that extended it provide support for both IPv4 and IPv6.
However, this support does not fully extend to the highly hybridized
environments that are characteristic of the transitional migratory
phase from IPv4 to IPv6 networks. During this phase, many server and
client implementations run on dual-stack hosts. In such
environments, a dual-stack host will likely suffer greater connection
delay, and by extension an inferior user experience, than an
IPv4-only host. The need to remedy this diminished performance of
dual-stack hosts led to the development of the Happy Eyeballs
[RFC6555] algorithm, which has since been implemented in many
protocols and applications.
This document updates the DNS lookup procedures of RFC 3263 [RFC3263]
in preparation for the specification of the application of Happy
Eyeballs to SIP. Happy Eyeballs will provide enhanced performance,
and consequently user experience, in highly hybridized dual-stack SIP
networks. The 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 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 algorithm and implementation and design considerations in
RFC 6555 [RFC6555] for more information about issues with setting up
dual-stack network flows.
Section 4 of this document clarifies the interaction of [RFC3263]
with [RFC6157] and [RFC6724].
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
RFC 3261 [RFC3261] defines additional terms used in this document
that are specific to the SIP domain such as "proxy", "registrar",
"redirect server", "user agent server" or "UAS", "user agent client"
or "UAC", "back-to-back user agent" or "B2BUA", "dialog",
"transaction", and "server transaction".
This document uses the term "SIP server" that is defined to include
the following SIP entities: user agent server, registrar, redirect
server, a SIP proxy in the role of user agent server, and a B2BUA in
the role of a user agent server.
Johansson, et al. Expires March 4, 2017 [Page 3]
Internet-Draft Locating SIP Servers in IPv4/IPv6 August 2016
While this document focuses on the dual-stack situation described in
RFC 6555 and other documents, concerning the migration from an
IPv4-only network to a network supporting both IPv4 and IPv6, the
techniques described can be used in other situations. Possible
situations include when a device has multiple interfaces with
distinct addressing characteristics and when additional IP address
families are created in the future. This document uses the general
term "dual-stack" to include all situations where the client has
access to multiple communication methods that have distinct
addressing characteristics.
The term "address records" means the DNS records which translate a
domain name into addresses within the address family(ies) that the
entity supports (as A records provide IPv4 addresses and AAAA records
provide IPv6 addresses), regardless of whether the address family was
defined before or after this document was approved.
3. DNS Procedures in a Dual-Stack Network
This specification introduces two normative DNS lookup procedures.
These are designed to improve the performance of dual-stack clients
in IPv4/IPv6 networks.
3.1. Dual-Stack SIP UA DNS Record Lookup Procedure
Once the transport protocol has been determined, the procedure for
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
Section 4.2 of RFC 3263 [RFC3263]. The piece relevant to this
discussion is:
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
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
transport protocol determined previously.
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
numeric IP address, and no port is present in the URI. The piece
relevant to to this discussion is:
If no SRV records were found, the client performs an A or AAAA
record lookup of the domain name. The result will be a list of IP
addresses, each of which can be contacted using the transport
protocol determined previously, at the default port for that
transport. Processing then proceeds as described above for an
explicit port once the A or AAAA records have been looked up.
Johansson, et al. Expires March 4, 2017 [Page 4]
Internet-Draft Locating SIP Servers in IPv4/IPv6 August 2016
Happy Eyeballs [RFC6555] documents that looking up the "A or AAAA
record" is not an effective practice for dual-stack clients and that
it can add significant connection delay and greatly degrade user
experience. Therefore, this document makes the following normative
addendum to the DNS lookup procedures of Section 4.2 of RFC 3263
[RFC3263] for IPv4/IPv6 hybrid SIP networks and recommends it as a
best practice for such dual-stack networks:
The dual-stack client SHOULD look up address records for all
address families that it supports for the domain name and add the
resulting addresses to the list of IP addresses to be contacted.
A client MUST be prepared for the existence of DNS resource
records containing addresses in families that it does not support;
if such records may be returned by the client's DNS queries, such
records MUST be ignored as unusable and the supported addresses
used as specified herein.
3.2. Indicating Address Family Preference in DNS SRV Records
The Happy Eyeballs algorithm [RFC6555] is particularly effective for
dual-stack HTTP client applications that have significant performance
differences between their IPv4 and IPv6 network paths. This is
because the client can initiate two TCP connections to the server,
one using IPv4 and one using IPv6, and then use the connection which
completes first. This works properly because the client can test
each route by initiating a TCP connection, but simply opening a TCP
connection to an HTTP server does not change the server's state; the
client will send the HTTP request on only one connection.
Unfortunately, in common SIP situations, it is not possible to "race"
simultaneous request attempts using two address families. If the SIP
requests are transmitted as single UDP packets, sending two copies of
the request to two different addresses risks having two copies of the
request propagating through the SIP network at the same time. The
difference between SIP and HTTP is that in SIP the sender cannot test
a route in a non-state-changing way.
(If two copies of the same request arrive at the destination client,
the client MUST reject the second of them with a 482 "Merged Request"
response.[RFC3261] But this rule is not sufficient to prevent user-
visible differences in behavior. A proxy that is upstream of the
second request to arrive at the client may (almost immediately!)
serially fork the second request to further destinations (e.g., the
voicemail service for the destination client).)
In this common 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 records to indicate such a preference for an address family.
Johansson, et al. Expires March 4, 2017 [Page 5]
Internet-Draft Locating SIP Servers in IPv4/IPv6 August 2016
This 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 wishes to do this can use the lowest SRV priority to
publish hostnames that only resolve in IPv6 and the next priority
with host names that resolve in both address families.
Note that hostnames that have addresses in only one address family
are discouraged by [RFC6555]. Such special-purpose hostnames SHOULD
be used only as described in this section, as targets of SRV records
for an aggregate host name, where the aggregate host name ultimately
resolves to addresses in all families supported by the client.
4. Clarification of Interaction with RFC 6724
Section 5 of [RFC6157] specifies that the addresses from the address
records for a single target DNS name for a server's DNS name must be
contacted in the order specified by the source and destination
address selection algorithms defined in [RFC6724]. The set of
addresses provided to a single invocation of the destination address
selection algorithm MUST be the address records for the target DNS
name in a single SRV record (or, if there are no SRV records, the DNS
name in the URI or derived via NAPTR) -- the destination address
selection algorithm MUST NOT reorder addresses derived from different
SRV records. Typically, desination address selection is done by
using the (relatively new) 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].
Thus, if SRV lookup on the server's DNS name is successful, the major
ordering of the complete list of destination addresses is determined
by the priority and weight fields of the SRV records (as specified in
[RFC2782]) and the (minor) ordering among the destinations derived
from the "target" field of a single SRV record is determined by
[RFC6724].
For example, consider a server with DNS name example.com, with TCP
transport specified. The relevant SRV records for example.com 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 processing of [RFC2782] results in this ordered list of target
domain names:
sip-1.example.com
sip-2.example.com
Johansson, et al. Expires March 4, 2017 [Page 6]
Internet-Draft Locating SIP Servers in IPv4/IPv6 August 2016
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.
Johansson, et al. Expires March 4, 2017 [Page 7]
Internet-Draft Locating SIP Servers in IPv4/IPv6 August 2016
5. Security Considerations
This document introduces two new normative procedures to the existing
DNS procedures used to locate SIP servers. A client may contact
additional target addresses for a URI beyond those prescribed in
[RFC3263], and/or it may contact target addresses in a different
order than prescribed in [RFC3263]. Neither of these changes
introduce any new security considerations because it has always been
assumed that a client desiring to send to a URI may contact any of
its targets that are listed in DNS.
The specific security vulnerabilities, attacks and threat models of
the various protocols discussed in this document (SIP, DNS, SRV
records, Happy Eyeballs requirements and algorithm, etc.) are well
documented in their respective specifications.
6. IANA Considerations
This document does not require any actions by IANA.
7. Acknowledgments
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
tests and discussions at SIPit events, organized by the SIP Forum.
This document has benefited from the expertise and review feedback of
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
authors wish to specifically call out the efforts and express their
gratitude for the detailed and thoughtful comments and corrections of
Dan Wing, Brett Tate, Rifaat Shekh-Yusef, Carl Klatsky, Mary Barnes,
Keith Drage, Cullen Jennings, Simon Perreault, Paul Kyzivat, Adam
Roach, Richard Barnes, Ben Campbell, Stefan Winter, Spencer Dawkins,
and Suresh Krishnan. Adam Roach devised the example in Section 4.
8. Revision History
[Note to RFC Editor: Please remove this entire section upon
publication as an RFC.]
8.1. Changes from draft-ietf-sipcore-dns-dual-stack-07 to draft-ietf-
sipcore-dns-dual-stack-08
Remove the reference to RFC 3484, since that RFC has been superseded,
and the reference was only the statement that 3484 had been
superseded by RFC 6724.
Johansson, et al. Expires March 4, 2017 [Page 8]
Internet-Draft Locating SIP Servers in IPv4/IPv6 August 2016
Added explanation why "racing" simultaneous copies of a SIP requests
causes incorrect behavior. Acknowledged Spencer Dawkins for this.
In Section 4, made explcit the ordered list of target domain names
that result from processing the SRV records. Acknowledged Suresh
Krishnan for suggesting this.
Updated the Terminology section to remove the definitions of
"IPv4-only", etc. (which weren't being used) and add a definition of
"dual-stack" that includes all multiple-stack situations.
8.2. Changes from draft-ietf-sipcore-dns-dual-stack-06 to draft-ietf-
sipcore-dns-dual-stack-07
Update per Ben Campbell's AD evaluation.
Update Vijay Gurbani's affiliation.
Update per Stefan Winter's OPS-DIR review.
8.3. Changes from draft-ietf-sipcore-dns-dual-stack-05 to draft-ietf-
sipcore-dns-dual-stack-06
Acknowledged Adam Roach for providing the example in Section 4.
Correct references to [RFC6157] vs. references to [RFC6724].
8.4. 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.
8.5. Changes from draft-ietf-sipcore-dns-dual-stack-03 to draft-ietf-
sipcore-dns-dual-stack-04
Changed the "updates" specification to add RFC 3263 and remove RFC
6157.
Added Simon Perreault to the acknowledgments.
Minor wording changes.
Johansson, et al. Expires March 4, 2017 [Page 9]
Internet-Draft Locating SIP Servers in IPv4/IPv6 August 2016
8.6. Changes from draft-ietf-sipcore-dns-dual-stack-02 to draft-ietf-
sipcore-dns-dual-stack-03
Described the relationship to RFC 3263 as "update", since the
existing wording in 3263 is not what we want. Arguably, the new
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.
Described the relationship to RFC 6157 as "clarification", since the
described interaction between 3263 and 6157 appears to be the only
reasonable interpretation.
Revised wording, punctuation, and capitalization in various places.
Clarified that this draft does not document Happy Eyeballs for SIP,
but is preparatory for it.
Attempted to use "update" for text that is definitively a change to
the preexisting text and "clarify" for text that is a more clear
statement of the (presumed) intention of the preexisting text.
Removed normative words from section 1, the introduction.
Copied definition of "address records" from RFC 2782 (SRV records) to
allow the specifications to expand automatically to include any new
address families.
Relocated the text requiring a client to ignore addresses that it
discovers in address families it does not support from section 4.2
(which describes why the situation arises) to section 4.1 (which
describes how clients look up RRs).
Clarified the interaction with RFC 6157 (source and destination
address selection in IPv6) to specify what must have been intended:
The major sort of the destinations is the ordering determined by
priority/weight in the SRV records; the addresses derived from a
single SRV record's target are minorly sorted based on RFC 6157.
Removed editor's name from the acknowledgments list.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
Johansson, et al. Expires March 4, 2017 [Page 10]
Internet-Draft Locating SIP Servers in IPv4/IPv6 August 2016
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
DOI 10.17487/RFC2782, February 2000,
<http://www.rfc-editor.org/info/rfc2782>.
[RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation
Protocol (SIP): Locating SIP Servers", RFC 3263,
DOI 10.17487/RFC3263, June 2002,
<http://www.rfc-editor.org/info/rfc3263>.
[RFC6157] Camarillo, G., El Malki, K., and V. Gurbani, "IPv6
Transition in the Session Initiation Protocol (SIP)",
RFC 6157, DOI 10.17487/RFC6157, April 2011,
<http://www.rfc-editor.org/info/rfc6157>.
[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
<http://www.rfc-editor.org/info/rfc6724>.
9.2. Informative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>.
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, DOI 10.17487/RFC6555, April
2012, <http://www.rfc-editor.org/info/rfc6555>.
Authors' Addresses
Olle E. Johansson
Edvina AB
Runbovaegen 10
Sollentuna SE-192 48
SE
Email: oej@edvina.net
Johansson, et al. Expires March 4, 2017 [Page 11]
Internet-Draft Locating SIP Servers in IPv4/IPv6 August 2016
Gonzalo Salgueiro
Cisco Systems
7200-12 Kit Creek Road
Research Triangle Park, NC 27709
US
Email: gsalguei@cisco.com
Vijay Gurbani
Bell Labs, Nokia Networks
1960 Lucent Lane
Rm 9C-533
Naperville, IL 60563
US
Email: vkg@bell-labs.com
Dale R. Worley (editor)
Ariadne Internet Services
738 Main St.
Waltham, MA 02451
US
Email: worley@ariadne.com
Johansson, et al. Expires March 4, 2017 [Page 12]
