[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-wing-http-new-tech) 00 01 draft-ietf-v6ops-happy-eyeballs

v6ops                                                            D. Wing
Internet-Draft                                            A. Yourtchenko
Intended status:  Standards Track                                  Cisco
Expires:  April 28, 2011                                October 25, 2010


     Happy Eyeballs: Trending Towards Success with Dual-Stack Hosts
                draft-wing-v6ops-happy-eyeballs-ipv6-01

Abstract

   This document describes how a dual-stack client can determine the
   functioning path to a dual-stack server.  This provides a seemless
   user experience during initial deployment of dual-stack networks and
   during outages of IPv4 or outages of IPv6.

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
   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 April 28, 2011.

Copyright Notice

   Copyright (c) 2010 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



Wing & Yourtchenko       Expires April 28, 2011                 [Page 1]

Internet-Draft          Happy Eyeballs Dual Stack           October 2010


   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.  Notational Conventions . . . . . . . . . . . . . . . . . . . .  3
   3.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  3
     3.1.  URIs and hostnames . . . . . . . . . . . . . . . . . . . .  4
     3.2.  IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Client Recommendations . . . . . . . . . . . . . . . . . . . .  4
     4.1.  IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     4.2.  Additional Considerations  . . . . . . . . . . . . . . . .  7
       4.2.1.  Additional Network and Host Traffic  . . . . . . . . .  7
       4.2.2.  Abandon Non-Winning Connections  . . . . . . . . . . .  8
       4.2.3.  Flush or Expire Cache  . . . . . . . . . . . . . . . .  8
       4.2.4.  Determining Address Type . . . . . . . . . . . . . . .  8
       4.2.5.  Debugging and Troubleshooting  . . . . . . . . . . . .  8
       4.2.6.  DNS Behavior . . . . . . . . . . . . . . . . . . . . .  9
       4.2.7.  Thread safe DNS resolvers  . . . . . . . . . . . . . .  9
       4.2.8.  Middlebox Issues . . . . . . . . . . . . . . . . . . .  9
       4.2.9.  Multiple Interfaces  . . . . . . . . . . . . . . . . .  9
     4.3.  Content Provider Recommendations . . . . . . . . . . . . .  9
     4.4.  Security Considerations  . . . . . . . . . . . . . . . . .  9
     4.5.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . 10
     4.6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . 10
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     5.2.  Informational References . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11

















Wing & Yourtchenko       Expires April 28, 2011                 [Page 2]

Internet-Draft          Happy Eyeballs Dual Stack           October 2010


1.  Introduction

   In order to use HTTP successfully over IPv6, it is necessary that the
   user enjoys nearly identical performance as compared to IPv4.  A
   combination of today's applications, IPv6 tunneling and IPv6 service
   providers, 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 or IPv4 is the most optimal to connect to a
   server.  The suggestions in this document provide a user experience
   which is superior to connecting to ordered IP addresses which is
   helpful during the IPv6/IPv4 transition with dual stack hosts.

   Following the procedures in this document, once a certain address
   family is successful, the application trends towards preferring that
   address family.  Thus, repeated use of the application DOES NOT cause
   repeated probes over both address families.

   While the application recommendations in this document are described
   in the context of HTTP clients ("web browsers"), but is useful and
   applicable to other time-sensitive 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 and IPv6.  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 slower than native IPv4 connectivity.





Wing & Yourtchenko       Expires April 28, 2011                 [Page 3]

Internet-Draft          Happy Eyeballs Dual Stack           October 2010


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 or IPv6 will only function if the other party is also using
   an 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 tunnels, and broken IPv6 peering.

           DNS Server                  Client                  Server
               |                          |                       |
         1.    |<--www.example.com A?-----|                       |
         2.    |<--www.example.com AAAA?--|                       |
         3.    |---192.0.2.1------------->|                       |
         4.    |---2001:dba::1----------->|                       |
         5.    |                          |                       |
         6.    |                          |--TCP SYN, IPv6--->X   |
         7.    |                          |--TCP SYN, IPv6--->X   |
         8.    |                          |--TCP SYN, IPv6--->X   |
         9.    |                          |                       |
         10.   |                          |--TCP SYN, IPv4------->|
         11.   |                          |<-TCP SYN+ACK, IPv4----|
         12.   |                          |--TCP ACK, IPv4------->|

                 Figure 1: Existing behavior message flow

   The client obtains the IPv4 and IPv6 records for the server (1-4).
   The client attempts to connect using IPv6 to the server, but the IPv6
   path is broken (6-8), which consumes several seconds of time.
   Eventually, the client attempts to connect using IPv4 (10) which
   succeeds.


4.  Client Recommendations

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



Wing & Yourtchenko       Expires April 28, 2011                 [Page 4]

Internet-Draft          Happy Eyeballs Dual Stack           October 2010


   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.

4.1.  IPv6

   If a TCP client supports IPv6 and IPv4 and is connected to IPv4 and
   IPv6 networks, it can perform the procedures described in this
   section.

           DNS Server                  Client                  Server
               |                          |                       |
         1.    |<--www.example.com A?-----|                       |
         2.    |<--www.example.com AAAA?--|                       |
         3.    |---192.0.2.1------------->|                       |
         4.    |---2001:dba::1----------->|                       |
         5.    |                          |                       |
         6.    |                          |==TCP SYN, IPv6===>X   |
         7.    |                          |--TCP SYN, IPv4------->|
         8.    |                          |<-TCP SYN+ACK, IPv4----|
         9.    |                          |--TCP ACK, IPv4------->|
        10.    |                          |==TCP SYN, IPv6===>X   |

               Figure 2: Happy Eyeballs flow 1, IPv6 broken

   In diagram above, the client sends two TCP SYNs at the same time over
   IPv6 (6) and IPv4 (7).  In the diagram, the IPv6 path is broken but
   has little impact to the user because there is no long delay before
   using IPv4.  The IPv6 path is retried until the application gives up
   (10).

           DNS Server                  Client                  Server
               |                          |                       |
         1.    |<--www.example.com A?-----|                       |
         2.    |<--www.example.com AAAA?--|                       |
         3.    |---192.0.2.1------------->|                       |
         4.    |---2001:dba::1----------->|                       |
         5.    |                          |                       |
         6.    |                          |==TCP SYN, IPv6=======>|
         7.    |                          |--TCP SYN, IPv4------->|
         8.    |                          |<=TCP SYN+ACK, IPv6====|
         9.    |                          |<-TCP SYN+ACK, IPv4----|
        10.    |                          |==TCP ACK, IPv6=======>|
        11.    |                          |--TCP ACK, IPv4------->|
        12.    |                          |--TCP RST, IPv4------->|

               Figure 3: Happy Eyeballs flow 2, IPv6 working




Wing & Yourtchenko       Expires April 28, 2011                 [Page 5]

Internet-Draft          Happy Eyeballs Dual Stack           October 2010


   The diagram above shows a case where both IPv6 and IPv4 are working,
   and IPv4 is abandoned (12).

   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 TCP client application 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 TCP client application 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

      *  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 4.2.2).



Wing & Yourtchenko       Expires April 28, 2011                 [Page 6]

Internet-Draft          Happy Eyeballs Dual Stack           October 2010


   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 TCP client
   applications 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.  Additional Considerations

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

4.2.1.  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 procedures described in this
   document retain a quality user experience while transitioning from
   IPv4-only to dual stack.  The quality user experience benefits the



Wing & Yourtchenko       Expires April 28, 2011                 [Page 7]

Internet-Draft          Happy Eyeballs Dual Stack           October 2010


   user but to the detriment of the network and server that are serving
   the user.

4.2.2.  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.

4.2.3.  Flush or Expire Cache

   Because every network has different characteristics (e.g., working or
   broken IPv6 connectivity) the IPv6/IPv4 preference value (P) SHOULD
   be reset to its default whenever the host is connected to a new
   network ([cx-osx], [cx-win]).  However, in some instances the
   application and the host are unaware the network connectivity has
   changed so it is RECOMMENDED that per-destination values expire after
   10 minutes of inactivity.

4.2.4.  Determining Address Type

   [[[ IS THIS SECTION NECESSARY ??

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

   ]]]

4.2.5.  Debugging and Troubleshooting

   This mechanism is aimed to help the user experience in case of
   connectivity problems.  However, this precise reason also makes it
   tougher to use these applications as a means of the verification that
   the problems are fixed.  To assist in that regard, the applications
   implementing the proposal in this document SHOULD also provide a
   mechanism to temporarily use only one address family.




Wing & Yourtchenko       Expires April 28, 2011                 [Page 8]

Internet-Draft          Happy Eyeballs Dual Stack           October 2010


4.2.6.  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.]]

4.2.7.  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.

4.2.8.  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.

4.2.9.  Multiple Interfaces

   Interaction of the suggestions in this document with multiple
   interfaces, and interaction with the MIF working group, is for
   further study.

4.3.  Content Provider Recommendations

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

4.4.  Security Considerations

   [[Placeholder.]]

   See Section 4.2.2.




Wing & Yourtchenko       Expires April 28, 2011                 [Page 9]

Internet-Draft          Happy Eyeballs Dual Stack           October 2010


4.5.  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 [RFC5245]), 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.

4.6.  IANA Considerations

   This document has no IANA actions.


5.  References

5.1.  Normative References

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

5.2.  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>.

   [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.

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

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              April 2010.



Wing & Yourtchenko       Expires April 28, 2011                [Page 10]

Internet-Draft          Happy Eyeballs Dual Stack           October 2010


   [cx-osx]   Adium, "AIHostReachabilityMonitor", June 2009,
              <https://bugzilla.redhat.com/show_bug.cgi?id=505105>.

   [cx-win]   Microsoft, "NetworkChange.NetworkAvailabilityChanged
              Event", June 2009, <http://msdn.microsoft.com/en-us/
              library/
              system.net.networkinformation.networkchange.networkavailab
              ilitychanged.aspx>.

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


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



















Wing & Yourtchenko       Expires April 28, 2011                [Page 11]


Html markup produced by rfcmarkup 1.108, available from http://tools.ietf.org/tools/rfcmarkup/