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Versions: 00 01 draft-wing-v6ops-happy-eyeballs-ipv6

Applications Area                                                D. Wing
Internet-Draft                                            A. Yourtchenko
Intended status:  Standards Track                           P. Natarajan
Expires:  February 21, 2011                                        Cisco
                                                         August 20, 2010


        Happy Eyeballs: Trending Towards Success (IPv6 and SCTP)
                      draft-wing-http-new-tech-01

Abstract

   People like their computers to work quickly.  During the transition
   to new technology, both old and new technologies have to peacefully
   co-exist.  However, if users experience connection delays attributed
   to the new technology the new technology will be shunned.

   HTTP ("The Web") is one of the most visible and time-critical
   applications that is used by nearly every Internet user.  It is
   critical that new technologies which improve HTTP not impair or delay
   the display of HTTP content.  It is also important that users retain
   the ability to share URIs amongst friends and colleagues, even if the
   other users have not upgraded to the new technology.

   This draft makes several recommendations to ensure user satisfaction
   and a smooth transition from HTTP's pervasive IPv4 to IPv6 and from
   TCP to SCTP.

   The audience for this draft is application developers and content
   providers.  This draft is discussed on the Applications Discuss
   mailing list, https://www.ietf.org/mailman/listinfo/apps-discuss.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at



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   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on February 21, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.






























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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Notational Conventions . . . . . . . . . . . . . . . . . . . .  4
   3.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  URIs and hostnames . . . . . . . . . . . . . . . . . . . .  5
     3.2.  IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.3.  SCTP . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  HTTP Client Recommendations  . . . . . . . . . . . . . . . . .  5
     4.1.  IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.2.  SCTP . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Additional Considerations  . . . . . . . . . . . . . . . . . .  9
     5.1.  Additional Network and Host Traffic  . . . . . . . . . . .  9
     5.2.  Abandon Non-Winning Connections  . . . . . . . . . . . . .  9
     5.3.  Flush or Expire Cache  . . . . . . . . . . . . . . . . . .  9
     5.4.  Determining Address Type . . . . . . . . . . . . . . . . .  9
     5.5.  DNS Behavior . . . . . . . . . . . . . . . . . . . . . . . 10
     5.6.  Thread safe DNS resolvers  . . . . . . . . . . . . . . . . 10
     5.7.  Middlebox Issues . . . . . . . . . . . . . . . . . . . . . 10
     5.8.  Multiple Interfaces  . . . . . . . . . . . . . . . . . . . 10
   6.  Content Provider Recommendations . . . . . . . . . . . . . . . 11
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 11
     10.2. Informational References . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13























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1.  Introduction

   In order to use HTTP successfully over IPv6 or SCTP, it is necessary
   that the user enjoys nearly identical performance as compared to
   their old technology (IPv4 and TCP).  A combination of today's
   applications, IPv6 tunneling and IPv6 service providers, IPv4 NAT,
   and some of today's content providers all cause the user experience
   to suffer (Section 3).  For IPv6, Google ensures a positive user
   experience by using a DNS white list of IPv6 service providers who
   peer directly with Google [whitelist].  However, this is not scalable
   to all service providers worldwide, nor is it scalable for other
   content providers to operate their own DNS white list.

   Instead, this document suggests a mechanism for applications to
   quickly determine if IPv6, IPv4, SCTP, or TCP is the most optimal to
   connect to a server.  The suggestions in this document provide a user
   experience which is superior to HTTP using TCP and IPv4, especially
   in IPv6/IPv4 transition environment with dual stack hosts (e.g.,
   [RFC4213], DS-Lite [I-D.ietf-softwire-dual-stack-lite], 6rd
   [I-D.despres-6rd]).

   Once a certain address family is successful, it trends towards
   preferring that address family.  Thus, repeated use of the
   application DOES NOT cause repeated probes over both address
   families.

   The application recommendations in this document are primarily for
   HTTP clients ("web browsers") and may also be helpful for other
   applications.


2.  Notational Conventions

   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 [RFC2119].


3.  Problem Statement

   As discussed in more detail in Section 3.1, it is important that the
   same URI and hostname be used for IPv4, IPv6, SCTP, and TCP.  Using
   separate namespaces causes namespace fragmentation and reduces the
   ability for users to share URIs and hostnames, and complicates
   printed material that includes the URI or hostname.

   As discussed in more detail in Section 3.2, IPv6 connectivity is
   sometimes broken entirely or, due to tunnel technologies might be



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   slower than native IPv4 connectivity.  However, due to port
   limitations inherent in stateful IPv6/IPv4 translators [BEHAVE], it
   is important that web browsers begin preferring IPv6 over IPv4 in
   order to avoid those port limitations.

   As discussed in more detail in Section 3.3, there is no standard
   mechanism to indicate a host supports a non-TCP transport protocol,
   such as SCTP.

3.1.  URIs and hostnames

   URIs are often used between users to exchange pointers to content --
   such as on Facebook, email, instant messaging, or other systems.
   Thus, production URIs and production hostnames containing references
   to IPv4, IPv6, TCP, or SCTP will only function if the other party
   also has application, OS, and a network that can access the URI or
   the hostname.

3.2.  IPv6

   When IPv6 connectivity is impaired, today's IPv6-capable web browsers
   incur many seconds of delay before falling back to IPv4.  This harms
   the user's experience with IPv6, which will slow the acceptance of
   IPv6, because IPv6 is frequently disabled in its entirety on the end
   systems to improve the user experience.

   Reasons for such failure include no connection to the IPv6 Internet,
   broken 6to4 or Teredo tunnel, and broken IPv6 peering.  To prevent
   this delay an experiment with IPv6 connectivity, content providers
   use a separate namespace for their web server (e.g.,
   ipv6.example.com), but doing that with production systems causes the
   problems described in Section 3.1.

3.3.  SCTP

   SCTP provides benefits over TCP [I-D.natarajan-http-over-sctp].

   Unlike IPv6 which has an AAAA record, there is no DNS query that
   indicates a host supports SCTP [RFC4960], and HTTP URI scheme is not
   extensible to support an SRV query that could provide such support.
   Even if there was, it isn't possible to determine if a middlebox,
   such as a firewall or a NAT, would block the SCTP association.


4.  HTTP Client Recommendations

   To provide fast connections for users, HTTP clients should make
   connections quickly over various technologies, automatically tune



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   itself to avoid flooding the network with unnecessary connections
   (i.e., for technologies that have not made successful connections),
   and occasionally flush its self-tuning.

   If an HTTP client supports IPv6 and SCTP (in addition to IPv4 and
   TCP), the procedures described in Section 4.1 and Section 4.2 are
   performed together.

4.1.  IPv6

   This section details how to provide robust dual stack service for
   both IPv6 and IPv4, so that the user perceives very fast application
   response.

   The HTTP client is configured with one value, P. A positive value
   indicates a preference for IPv6 and a negative value indicates a
   preference for IPv4.  A value of 0 indicates equal weight, which
   means the A and AAAA queries and associated connection attempts will
   be sent as quickly as possible.  The absolute value of P is the
   measure of a delay before initiating a connection attempt on the
   other address family.  There are two P values maintained:  one is
   application-wide and the other is specific per each destination
   (hostname and port).

   The algorithm attempts to delay the DNS query until it expects that
   address family will be necessary; that is, if the preference is
   towards IPv6, then AAAA will be queried immediately and the A query
   will be delayed.

   The HTTP client starts two threads in order to minimize the user-
   noticeable delay ("dead time") during the connection attempts:

   thread 1: (IPv6)

      *  If P<0, wait for absolute value of p*10 milliseconds

      *  send DNS query for AAAA

      *  wait until DNS response is received

      *  Attempt to connect over IPv6 using TCP

   thread 2: (IPv4)

      *  if P>0, wait for p*10 milliseconds

      *  send DNS query for A




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      *  wait until DNS response is received

      *  Attempt to connect over IPv4 using TCP

   The first thread that succeeds returns the completed connection to
   the parent code and aborts the other thread (Section 5.2).

   After a connection is successful, we want to adjust the application-
   wide preference and the per-destination preference.  The value of P
   is incremented (decremented) each time an IPv6 (IPv4) connection is
   successfully made.  When a connection using the less-preferred
   address family is successful, it indicates the wrong address family
   was used and the P is halved:

   o  If P>0 (indicating IPv6 is preferred over IPv4) and the first
      thread to finish was the IPv6 thread it indicates the IPv6
      preference is correct and we need to re-enforce this by increasing
      the application-wide P value by 1.  However, if the first thread
      to finish was the IPv4 thread it indicates an IPv6 connection
      problem occurred and we need to aggressively prefer IPv4 more by
      halving P and rounding towards 0.

   o  If P<0 (indicating IPv4 is preferred over IPv6) and the first
      thread to finish was the IPv4 thread it indicates the preference
      is correct and we need to re-enforce this gently by decreasing the
      application-wide P value by 1.  However, if the first thread to
      finish was the IPv6 thread it indicates an IPv4 connection problem
      and we need to aggressively avoid IPv4 by halving P and rounding
      towards 0.

   o  If P=0 (indicating equal preference), P is incremented if the
      first thread to complete was the IPv6 thread, or decremented if
      the first thread to complete was the IPv4 thread.

   After adjusting P, it should never be larger than 4 seconds -- which
   is similar to the value used by many IPv6-capable HTTP clients to
   switch to an alternate A or AAAA record.

      Note:  Proof of concept tests on fast networks show that even
      smaller value (around 0.5 seconds) is practical.  More extensive
      testing would be useful to find the best upper boundary that still
      ensures a good user experience.

4.2.  SCTP

   Due to the proliferation of NATs on the IPv4 Internet the best
   success for SCTP can be achieved by attempting both native SCTP
   connections and SCTP-over-UDP [I-D.tuexen-sctp-udp-encaps]



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   connections.

   For SCTP the following parameters are used:

   SWAIT:  Application-wide wait time for an SCTP association attempt to
           complete.  Default value of 50ms is RECOMMENDED.

   PREF:   This denotes per-destination transport preference.  Possible
           values are "TCP", "SCTP", and "BOTH".  Default value of
           "BOTH" is RECOMMENDED.

   The HTTP client starts several threads in order to minimize the user-
   noticeable delay ("dead time") during the connection attempts.  The
   client starts one or more threads based on the following logic:

   If ((PREF == BOTH) or (PREF == SCTP)) start thread 1.  If making a
   connection using IPv4 start thread 2.

   If ((PREF == BOTH) or (PREF == TCP)) start thread 3.

     thread 1 (SCTP):

      *  Attempt to connect using SCTP (i.e., send SCTP INIT)

     thread 2 (SCTP over UDP):

      *  Attempt to connect using SCTP over UDP (i.e., send SCTP INIT
         over UDP)

     thread 3 (TCP):

      *  Attempt to connect using TCP

   If an SCTP association attempt was made by a thread, the HTTP client
   waits for at least K ms; K = max(SWAIT, time taken for the TCP
   connection to complete).  If the TCP connection finishes during this
   wait period, the HTTP client MAY choose TCP for the current HTTP
   transfer but MUST wait until K ms to figure if the SCTP association
   can be completed.

   If the HTTP client did not choose TCP during the wait period and the
   SCTP association completes successfully, the HTTP client prefers SCTP
   over TCP connections and abandons the TCP connection.

   After a connection is successful, we want to adjust the per-
   destination preference for this destination.  It is not recommended
   to dynamically adjust the application-wide default value for SWAIT.
   If the SCTP association was successful, set destination's



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   PREF="SCTP", else set PREF="TCP".


5.  Additional Considerations

   This section discusses considerations and requirements that are
   common to new technology deployment.

5.1.  Additional Network and Host Traffic

   Additional network traffic and additional server load is created due
   to these recommendations and mitigated by application-wide and per-
   destination timer adjustments.  The intent of this document is to
   show how good user experience can be maintained while the
   transitioning from IPv4 to IPv6, and transitioning from TCP to SCTP.
   The good user experience is to the benefit of the user but to the
   detriment of the network and server that are serving the user.

5.2.  Abandon Non-Winning Connections

   It is RECOMMENDED that the non-winning connections be abandoned, even
   though they could be used to download content.  This is because some
   web sites provide HTTP clients with cookies (after logging in) that
   incorporate the client's IP address, or use IP addresses to identify
   users.  If some connections from the same HTTP client are arriving
   from different IP addresses, such HTTP applications will break.

      Editor's note:  If we can provide guidance to IPv6 and SCTP
      developers that connections from the same client could arrive on
      IPv4, IPv6, TCP, and SCTP we could eliminate the above paragraph.
      But could we be sure all web sites would follow such guidance?

5.3.  Flush or Expire Cache

   Because every network has different characteristics (working or
   broken IPv6 connectivity, middlebox that permits or blocks SCTP,
   etc.) the IPv6/IPv4 preference value (P) and the SCTP parameters
   (SWAIT and PREF) SHOULD be reset to their default whenever the host
   is connected to a new network.  However, in some instances the
   application and the host are unaware the network connectivity has
   changed (e.g., when behind a NAT) so it is RECOMMENDED that per-
   destination values expire after 10 minutes of inactivity.

5.4.  Determining Address Type

   [[[ IS THIS SECTION NECESSARY ??

   For some transitional technologies such as a dual-stack host, it is



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   easy for the application to recognize the native IPv6 address
   (learned via a AAAA query) and the native IPv4 address (learned via
   an A query).  For other transitional technologies [RFC2766] it is
   impossible for the host to differentiate a transitional technology
   IPv6 address from a native IPv6 address (see Section 4.1 of
   [RFC4966]).  Replacement transitional technologies are attempting to
   bridge this gap.  It is necessary for applications to distinguish
   between native and transitional addresses in order to provide the
   most seamless user experience.

   ]]]

5.5.  DNS Behavior

   Unique to DNS AAAA queries are the problems described in [RFC4074]
   which, if they still persist, require applications to perform an A
   query before the AAAA query.

      [[Editor's Note:  It is believed these defective DNS servers have
      long since been upgraded.  If so, we can remove this section.]]

5.6.  Thread safe DNS resolvers

   Some applications and some OSs do not have thread safe DNS resolvers,
   which complicates implementation of simultaneous A and AAAA queries
   for IPv4/IPv6.

5.7.  Middlebox Issues

   Some devices are known to exhibit what amounts to a bug, when the A
   and AAAA requests are sent back-to-back over the same 4-tuple, and
   drop one of the requests or replies [DNS-middlebox].  However, in
   some cases fixing this behaviour may not be possible either due to
   the architectural limitations or due to the administrative
   constraints (location of the faulty device is unknown to the end
   hosts or not controlled by the end hosts).  The algorithm described
   in this draft, in the case of this erroneous behaviour will
   eventually pace the queries such that this issue is will be avoided.
   The algorithm described in this draft also avoids calling the
   operating system's getaddrinfo() with "any", which should prevent the
   operating system from sending the A and AAAA queries on the same
   port.

5.8.  Multiple Interfaces

   Interaction of the suggestions in this document with multiple
   interfaces is for further study.




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6.  Content Provider Recommendations

   Content providers SHOULD provide both AAAA and A records for servers
   using the same DNS name for both IPv4 and IPv6.


7.  Security Considerations

   [[Placeholder.]]

   See Section 5.2.


8.  Acknowledgements

   The mechanism described in this paper was inspired by Stuart
   Cheshire's discussion at the IAB Plenary at IETF72, the author's
   understanding of Safari's operation with SRV records, Interactive
   Connectivity Establishment (ICE [I-D.ietf-mmusic-ice]), and the
   current IPv4/IPv6 behavior of SMTP mail transfer agents.

   Thanks to Fred Baker, Jeff Kinzli, Christian Kuhtz, and Iljitsch van
   Beijnum for fostering the creation of this document.

   Thanks to Scott Brim and Stig Venaas for providing feedback on the
   document.


9.  IANA Considerations

   This document has no IANA actions.


10.  References

10.1.  Normative References

   [I-D.tuexen-sctp-udp-encaps]
              Tuexen, M. and R. Stewart, "UDP Encapsulation of SCTP
              Packets", draft-tuexen-sctp-udp-encaps-05 (work in
              progress), July 2010.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol",
              RFC 4960, September 2007.




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10.2.  Informational References

   [DNS-middlebox]
              Various, "DNS middlebox behavior with multiple queries
              over same source port", June 2009,
              <https://bugzilla.redhat.com/show_bug.cgi?id=505105>.

   [I-D.despres-6rd]
              Despres, R., "IPv6 Rapid Deployment on IPv4
              infrastructures (6rd)", draft-despres-6rd-03 (work in
              progress), April 2009.

   [I-D.ietf-mmusic-ice]
              Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols",
              draft-ietf-mmusic-ice-19 (work in progress), October 2007.

   [I-D.ietf-softwire-dual-stack-lite]
              Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", draft-ietf-softwire-dual-stack-lite-06 (work
              in progress), August 2010.

   [I-D.natarajan-http-over-sctp]
              Natarajan, P., Amer, P., Leighton, J., and F. Baker,
              "Using SCTP as a Transport Layer Protocol for HTTP",
              draft-natarajan-http-over-sctp-02 (work in progress),
              July 2009.

   [RFC2766]  Tsirtsis, G. and P. Srisuresh, "Network Address
              Translation - Protocol Translation (NAT-PT)", RFC 2766,
              February 2000.

   [RFC4074]  Morishita, Y. and T. Jinmei, "Common Misbehavior Against
              DNS Queries for IPv6 Addresses", RFC 4074, May 2005.

   [RFC4213]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
              for IPv6 Hosts and Routers", RFC 4213, October 2005.

   [RFC4966]  Aoun, C. and E. Davies, "Reasons to Move the Network
              Address Translator - Protocol Translator (NAT-PT) to
              Historic Status", RFC 4966, July 2007.

   [whitelist]
              Google, "Google IPv6 DNS Whitelist", March 2008,
              <http://www.google.com/intl/en/ipv6>.




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Authors' Addresses

   Dan Wing
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email:  dwing@cisco.com


   Andrew Yourtchenko
   Cisco Systems, Inc.
   De Kleetlaan, 7
   San Jose, Diegem  B-1831
   Belgium

   Email:  ayourtch@cisco.com


   Preethi Natarajan
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email:  prenatar@cisco.com
























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