Happy EarBalls: Success with Dual-Stack, Connection-Oriented SIP
draft-worley-sip-he-connection-00

SIPCORE                                                     O. Johansson
Internet-Draft                                                 Edvina AB
Intended status: Standards Track                            G. Salgueiro
Expires: June 15, 2017                                     Cisco Systems
                                                               D. Worley
                                                                 Ariadne
                                                       December 12, 2016

    Happy EarBalls: Success with Dual-Stack, Connection-Oriented SIP
                   draft-worley-sip-he-connection-00

Abstract

   The Session Initiation Protocol (SIP) supports multiple transports
   running both over IPv4 and IPv6 protocols.  In more and more cases, a
   SIP user agent (UA) is connected to multiple network interfaces.  In
   these cases setting up a connection from a dual stack client to a
   dual stack server may suffer from the issues described in RFC 6555
   [RFC6555] ("Happy Eyeballs") - significant delays in the process of
   setting up a working flow to a server.  This negatively affects user
   experience.

   This document builds on RFC 6555 and explains how a [RFC3261]
   compliant SIP implementation can minimize delays when contacting a
   host name (obtained by using DNS NAPTR and SRV lookups) in a dual
   stack network using connection-oriented transport protocols.

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 June 15, 2017.

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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
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   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 and Conventions Used in This Document . . . . . .   3
   3.  DNS Procedures in a Dual-Stack Network  . . . . . . . . . . .   4
   4.  Establishing a Connection . . . . . . . . . . . . . . . . . .   5
     4.1.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   6
       4.1.1.  Address Preferences . . . . . . . . . . . . . . . . .   6
       4.1.2.  Stateful Behavior . . . . . . . . . . . . . . . . . .   6
       4.1.3.  Reset on Network (Re-)Initialization  . . . . . . . .   7
       4.1.4.  Abandon Non-Winning Connections . . . . . . . . . . .   7
   5.  Using an Existing Connection  . . . . . . . . . . . . . . . .   7
   6.  Additional Considerations . . . . . . . . . . . . . . . . . .   8
     6.1.  Preemtive Actions . . . . . . . . . . . . . . . . . . . .   8
     6.2.  Determining the Type of an Address  . . . . . . . . . . .   8
     6.3.  Debugging and Troubleshooting . . . . . . . . . . . . . .   9
     6.4.  Three or More Interfaces  . . . . . . . . . . . . . . . .   9
     6.5.  Multiple A and AAAA Resource Records  . . . . . . . . . .   9
     6.6.  Connection Timeout  . . . . . . . . . . . . . . . . . . .  10
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   9.  History . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Changes from draft-johansson-sip-he-connection-01 to
           draft-worley-sip-he-connection-00 . . . . . . . . . . . .  10
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     10.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

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1.  Introduction

   The Session Initiation Protocol (SIP) [RFC3261] and the documents
   that extended it provide support for both IPv4 and IPv6.  However,
   this support has problems with 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 revises the the [RFC3263] procedures to apply the
   "Happy Eyeballs" framework.  A dual-stack client using connection-
   oriented transport should set up multiple connections in parallel, to
   targets based on the result of DNS queries.  This document starts at
   the point where a SIP implementation has a host name that resolves
   using A and AAAA records.  Such a host name can either be the host
   part of a SIP URI (possibly including a port number) or the result of
   a lookup using DNS NAPTR and SRV records as described in RFC 3263 (as
   updated by RFC 7984[RFC7984]).

   Procedures for connectionless transport protocols for SIP are outside
   the scope of this document.  Procedures allowing a client to change
   the order of contacting targets that were derived from different host
   names are outside the scope of this document.

   The concepts in this document are elaborated from those developed in
   [RFC6555], and so some background information in RFC 6555 is not
   repeated here.  The reader is encouraged to read the available
   documentation regarding implementations of RFC 6555, as well as study
   Open Source implementations, in order to learn from the experience
   accumulated since the publishing of RFC 6555 in 2012.

2.  Terminology and Conventions Used in This Document

   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"; "server transaction".

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   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.

   This document also uses the following terminology to make clear
   distinction between SIP entities supporting only IPv4, only IPv6 or
   supporting both IPv4 and IPv6.

   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
      addresses.

   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
      addresses.

   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
      (and will be referred to in this document) as a "dual-stack"
      [RFC4213] UA/UAC/UAS.

   Discussion: Do we need special handling of websocket transport?

   While this document uses the term "dual-stack" based on RFC 6555 and
   earlier terminology, the authors acknowledge that the same solution
   can be applied to multi-interface environments as well as future
   versions of IP alongside with the current ones.

3.  DNS Procedures in a Dual-Stack Network

   A SIP client uses DNS to find a server based on a SIP URI.  This
   process is described in [RFC3263] and updated in [RFC7984].  Using
   this process, a list of "targets" is constructed, where each target
   consists of an IP address, a port number, and a protocol (e.g., TCP,
   UDP, TLS) by which to contact that address/port.  The process
   proceeds by constructing a sequence of host names, possibly by
   looking up NAPTR and/or SRV DNS records, and then for each host name
   looking up DNS address records (for all address families supported by
   the client) to generate the list of IP addresses for targets that are
   derived from that host name.  The addresses for each host name are
   ordered using the client's destination selection rules[RFC6724].  The
   sorted targets for all the host names are then concatenated into the
   sequence of targets to which the client will attempt to send the SIP
   message.

   Previously, the client contacts the targets in order until one is
   contacted successfully.  In order to contact a target, the client

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   establishes a transport connection (if necessary), sends the message
   using the transport (possibly resending the message several times),
   and then (for requests) waits for a response (either provisional or
   final).  The process ends successfully if the client receives a
   response.  The process ends unsuccessfully if the client receives a
   permanent error from the transport layer or if a SIP timer (Timer B
   or Timer F in [RFC3261]) expires.  Timeouts generally default to 32
   seconds.

   If the user has to wait for even one timeout, this will seriously
   degrade the user experience.  Thus, it is desirable to minimize the
   number of times the client has timeouts when sending requests.

   If the target list contains both IPv6 addresses and IPv4 addresses,
   this procedure can degrade the user's experience in common
   situations.  Typically, this problem arises when the client has an
   IPv6 interface, the server's preferred address is an IPv6 address,
   but the transit networks between the client and server do not carry
   IPv6.  This can cause the client to attempt to send a SIP request for
   32 seconds before it times out that target and continues with an IPv4
   target.  This problem parallels a problem that was widely seen in web
   browsers that was cured by specifying that web browsers should use a
   "Happy Eyeballs" algorithm[RFC6555] to determine the order in which
   to contact target addresses.

   This document specifies an amendment to these procedures, by which
   the subsequences of targets derived from individual host names may be
   contacted in a different order than is specified by the destination
   selection rules.  As in [RFC6555], the algorithm that the client uses
   is not specified by this document, but this document places
   requirements on the algorithm that improve the user's experience
   without unduly burdening the Internet infrastructure.  By analogy
   with the name "Happy Eyeballs" for similar algorithms in web
   browsers, we label these algorithms "Happy EarBalls"[UD].

   This document modifies the transport procedures only in the case when
   all targets for a host name have connection-oriented protocols
   (currently, TCP and TLS).  Other cases are outside the scope of this
   document.

4.  Establishing a Connection

   This section discusses the situation that most closely resembles RFC
   6555, which is when the SIP client has no active connection to any of
   the targets in a subsequence of targets derived from one host name.
   This specification allows the client to attempt to send a request to
   targets in the subsequence in a different order than is prescribed by
   RFC 3262 and RFC 6724.  In addition, this specification allows the

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   client to attempt to initiate a connection to a target without
   subsequently sending a request to the target.  However, the algorithm
   which the client uses use meet the constraints in this section.

   Typically, the SIP client will set up two connections, with some head
   start for one address family (which is possibly be configurable) and
   then select the first completed connection for use and close the
   other one.  The SIP message is sent on the selected connection only.

   The reason for this approach is to avoid the timeout associated with
   sending an unsuccessful SIP request, requiring the client to wait for
   a timeout before the request can be sent on a connection to another
   target - which in the case of SIP with default timers is 32 seconds.
   Waiting for timeout before trying with a second address will lead to
   a very poor user experience.

4.1.  Requirements

   The following requirements apply to any implementation that takes
   advantage of the relaxed requirements on message transmission
   specified by this document.

4.1.1.  Address Preferences

   An implementation MUST prefer the first IP address family returned by
   the host's address preference policy, unless it implements a stateful
   algorithm as described in Section 4.1.2.  This usually means giving
   preference to IPv6 over IPv4, although that preference can be
   overridden by user configuration or by network configuration.  If the
   host's policy is unknown or not attainable, the implementation MUST
   prefer IPv6 over IPv4.

4.1.2.  Stateful Behavior

   The algorithm may be stateful -- that is, the algorithm will remember
   that IPv6 always fails, or that IPv6 to certain prefixes always
   fails, and so on.  This section constrains such algorithms.
   Stateless algorithms, which do not remember the success/failure of
   previous connections, are not discussed in this section.

   After making a connection attempt using the preferred address family
   (e.g., IPv6) and failing to establish a connection within a certain
   time period (see Section 6.6), a Happy EarBalls implementation will
   decide to initiate a second connection attempt using the same address
   family or the other address family.

   Such an implementation MAY make prioritize making subsequent
   connection attempts (to the same host or to other hosts) using the

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   successful address family (e.g., IPv4).  So long as new connections
   are being attempted by the host, such an implementation MUST
   occasionally make connection attempts using the host's preferred
   address family, as that family may have become functional again, and
   the client SHOULD do so every 10 minutes.  The 10-minute delay before
   retrying a failed address family avoids the simple doubling of
   connection attempts on both IPv6 and IPv4.  This can be achieved by
   flushing Happy EarBalls state every 10 minutes, which does not
   significantly harm the application's subsequent connection setup
   time.  If connections using the preferred address family are again
   successful, the preferred address family MUST be used for subsequent
   connections.  Because this implementation is stateful, it MAY track
   connection success (or failure) based on IPv6 or IPv4 prefix (e.g.,
   connections to the same prefix assigned to the interface are
   successful whereas connections to other prefixes are failing).

4.1.3.  Reset on Network (Re-)Initialization

   Because every network has different characteristics (e.g., working or
   broken IPv6 or IPv4 connectivity), a Happy EarBalls algorithm SHOULD
   re-initialize when the interface is connected to a new network.
   Interfaces can determine network (re-)initialization by a variety of
   mechanisms (e.g., Detecting Network Attachment in IPv4 (DNAv4)
   [RFC4436], DNAv6 [RFC6059]).

4.1.4.  Abandon Non-Winning Connections

   Non-winning connections SHOULD be abandoned, even though they could
   -- in some cases -- be put to reasonable use.

   Justification: This reduces the load on the server (file descriptors,
   TCP control blocks) and stateful middleboxes (NAT and firewalls).
   Also, if the abandoned connection is IPv4, this reduces IPv4 address
   sharing contention.

   (There are some unlikely situations where a non-winning connection
   could be useful in the future: If at a later time, the client must
   send a request to a different host name, but one which has as a
   target the peer of the non-winning connection and does not have as a
   target the peer of the winning connection.)

5.  Using an Existing Connection

   When a client desires to send a message to a target that is within a
   subsequence of targets derived from one host name, the client may
   already have a connection established to one of the targets through
   either SIP Outbound[RFC5626] or the procedures of Section 4.  The
   client SHOULD attempt to send the message using the existing

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   connection in preference to using a new connection to one of the
   targets.

   If, in the client's operational environment, there is a significant
   risk that the connection has become unusable without the client
   becoming aware of it, the client SHOULD consider testing whether the
   connection is usable before sending the message using the connection.
   Some possible ways to probe a connection to determine if it is still
   usable are:

   o  Send a keep-alive, as specified by the protocol of the connection.

   o  Send a CR-LF-CR-LF keep-alive on a SIP Outbound
      connection[RFC5626].

   o  Send an OPTIONS request with "Max-Forwards: 0".

   (Note that a probe using an OPTIONS request can be used with any
   protocol.  If the OPTIONS reaches the target, the target is required
   to respond with either a 200 or 483 response[RFC3261] without
   forwarding it to another entity.  Conveniently, a server can respond
   to such a request statelessly, so such requests are low-overhead.
   (Although the [RFC5626] keep-alive methods have even lower
   overhead.))

6.  Additional Considerations

   This section discusses additional considerations related to Happy
   EarBalls.

6.1.  Preemtive Actions

   A client may be in a situation where it has advance notice that it is
   likely to need to send a message to a particular host name, for
   instance, if the user of a UA begins dialing an outgoing call which
   will be routed through a particular outgoing proxy.  In such a
   situation, the client SHOULD consider preemptively establishing a
   connection (Section 4) or probing an existing connection (Section 5).

6.2.  Determining the Type of an Address

   For some transitional technologies, such as a dual-stack host, it is
   easy for the application to recognize a native IPv6 address (learned
   via a AAAA query) and a native IPv4 address (learned via an A query).
   The use of IPv6/IPv4 translation in the local network makes it
   difficult or impossible to determine the address family by which the
   connection will traverse the global network.  However, IPv6/IPv4
   translators do not need to be deployed on networks with dual-stack

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   clients because dual-stack clients can use their native IP address
   family.  Environments where IPv6/IPv4 translation is active will
   degrade the ability of Happy EarBalls algorithms to establish working
   connections.

6.3.  Debugging and Troubleshooting

   Happy EarBalls is aimed at ensuring a reliable user experience
   regardless of connectivity problems affecting any single transport.
   However, this naturally means that applications employing these
   techniques are by default less useful for diagnosing issues with a
   particular address family.  To assist in that regard, an
   implementation MAY provide a mechanism to disable their Happy
   EarBalls behavior via a user setting, and to provide data useful for
   debugging (e.g., a log or way to review current preferences).

6.4.  Three or More Interfaces

   A dual-stack host normally has two logical interfaces: an IPv6
   interface and an IPv4 interface.  However, a dual-stack host might
   have more than two logical interfaces because of a VPN (where a third
   interface is the tunnel address, often assigned by the remote
   corporate network), because of multiple physical interfaces such as
   wired and wireless Ethernet, because the host belongs to multiple
   VLANs, or other reasons.  Optimal operation of Happy EarBalls with
   more than two logical interfaces is for further study and is outside
   the scope of this document.

6.5.  Multiple A and AAAA Resource Records

   It is possible that a DNS query for an A or AAAA resource record will
   return more than one A or AAAA address.  When this occurs, it is
   RECOMMENDED that a Happy EarBalls implementation order the responses
   following the host's address preference policy and then try the first
   target.  If that fails after a certain time (see Section 6.6), the
   next target SHOULD be chosen from the other address family.

   If the second attempt fails to connect, a Happy EarBalls
   implementation SHOULD try the other targets; the order of these
   connection attempts is not important.

   On the Internet today, servers commonly have multiple A records to
   provide load-balancing across their servers.  This same technique
   would be useful for AAAA records, as well.  However, if multiple AAAA
   records are returned to a client that is not using Happy EarBalls and
   that has broken IPv6 connectivity, the multiple AAAA records will
   further increase the delay to fall back to IPv4.  Thus, SIP server
   operators with native IPv6 connectivity SHOULD NOT offer multiple

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   AAAA records.  If Happy EarBalls is widely deployed in the future,
   this recommendation might be revisited.

6.6.  Connection Timeout

   The primary purpose of Happy EarBalls is to reduce the wait time for
   a dual-stack connection to complete, especially when the IPv6 path is
   broken and IPv6 is preferred.  Using a short timeout between
   initiating an IPv6 connection and initiating an IPv4 connection (on
   the order of tens of milliseconds) achieves this goal, but at the
   cost of network traffic.  This network traffic may be billable on
   certain networks, will create state on some middleboxes (e.g.,
   firewalls, intrusion detection systems, NATs), and will consume ports
   if IPv4 addresses are shared.  For these reasons, it is RECOMMENDED
   that connection attempts be paced to give connections a chance to
   complete.  It is RECOMMENDED that connection attempts be paced
   150-250 ms apart to balance human factors against network load.  A
   stateful algorithm MAY be more aggressive (that is, make connection
   attempts closer together), if it maintains estimates of the expected
   connection completion times.

7.  Security Considerations

   This document places additional restrictions on the existing
   procedures in the SIP protocol.  The specific security
   vulnerabilities, attacks and threat models of the various protocols
   discussed in this document (SIP, DNS, SRV records, etc.) are well-
   documented in their respective specifications.

8.  IANA Considerations

   This document does not require any actions by IANA.

9.  History

   Note to RFC Editor: Upon publication, remove this section.

9.1.  Changes from draft-johansson-sip-he-connection-01 to draft-worley-
      sip-he-connection-00

   This version has a different name for technical reasons.  It is, in
   reality, the successor to draft-johansson-sip-he-connection-01.

   Move Acknowledgments after References, as that is the style the
   Editor prefers.

   Updated Security Considerations: This increment of the H.E. work does
   not make normative changes in existing SIP.

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   Copy a lot of text from RFC 6555, as this I-D is parallel to RFC
   6555.

   Changed "hostname" to "host name", as the latter form is more common
   in RFCs by a moderate margin.

   Revised some of the introduction text to parallel the introduction of
   RFC 7984.

   Changed name of algorithm to "Happy EarBalls", added reference to
   Urban Dictionary.

   Many expansions of the discussion and revisions of the wording.

10.  References

10.1.  Normative References

   [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>.

10.2.  Informative 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>.

   [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>.

   [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>.

   [RFC4213]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
              for IPv6 Hosts and Routers", RFC 4213,
              DOI 10.17487/RFC4213, October 2005,
              <http://www.rfc-editor.org/info/rfc4213>.

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   [RFC5626]  Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed.,
              "Managing Client-Initiated Connections in the Session
              Initiation Protocol (SIP)", RFC 5626,
              DOI 10.17487/RFC5626, October 2009,
              <http://www.rfc-editor.org/info/rfc5626>.

   [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>.

   [RFC7984]  Johansson, O., Salgueiro, G., Gurbani, V., and D. Worley,
              Ed., "Locating Session Initiation Protocol (SIP) Servers
              in a Dual-Stack IP Network", RFC 7984,
              DOI 10.17487/RFC7984, September 2016,
              <http://www.rfc-editor.org/info/rfc7984>.

   [UD]       The Jews Who Stole Christmas, , "Urban Dictionary, entry
              'Earballs'", December 2011,
              <http://www.urbandictionary.com/define.php?term=Earballs>.

Acknowledgements

   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.

   Most of the material in Section 4.1 is taken from [RFC6555], whose
   authors are Dan Wing and Andrew Yourtchenko.

Authors' Addresses

   Olle E. Johansson
   Edvina AB
   Runbovaegen 10
   Sollentuna  SE-192 48
   SE

   Email: oej@edvina.net

   Gonzalo Salgueiro
   Cisco Systems
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709
   US

   Email: gsalguei@cisco.com

Johansson, et al.         Expires June 15, 2017                [Page 12]
Internet-Draft     Connection-Oriented Happy EarBalls      December 2016

   Dale R. Worley
   Ariadne Internet Services
   738 Main St.
   Waltham, MA  02451
   US

   Email: worley@ariadne.com

Johansson, et al.         Expires June 15, 2017                [Page 13]