v6ops D. Wing
Internet-Draft A. Yourtchenko
Intended status: Standards Track Cisco
Expires: April 16, 2011 October 13, 2010
Happy Eyeballs: Trending Towards Success with Dual-Stack Hosts
draft-wing-v6ops-happy-eyeballs-ipv6-00
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 IPv4 to IPv6 with dual-stack hosts.
The audience for this draft is application developers and content
providers. This draft is discussed on the v6oops mailing list,
https://www.ietf.org/mailman/listinfo/v6ops.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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The list of Internet-Draft Shadow Directories can be accessed at
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This Internet-Draft will expire on April 16, 2011.
Copyright Notice
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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
4. HTTP Client Recommendations . . . . . . . . . . . . . . . . . 5
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 . . . . . . . . . . . 7
4.2.3. Flush or Expire Cache . . . . . . . . . . . . . . . . 7
4.2.4. Determining Address Type . . . . . . . . . . . . . . . 8
4.2.5. Debugging and Troubleshooting . . . . . . . . . . . . 8
4.2.6. DNS Behavior . . . . . . . . . . . . . . . . . . . . . 8
4.2.7. Thread safe DNS resolvers . . . . . . . . . . . . . . 8
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 . . . . . . . . . . . . . . . . . . . . . 9
4.6. IANA Considerations . . . . . . . . . . . . . . . . . . . 10
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Normative References . . . . . . . . . . . . . . . . . . . 10
5.2. Informational References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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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.
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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.
4. HTTP Client Recommendations
To provide fast connections for users, HTTP clients should make
connections quickly over various technologies, automatically tune
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 an HTTP client supports IPv6 and IPv4 and is connected to IPv4 and
IPv6 networks, it can perform the procedures described in this
section.
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).
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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
* 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).
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
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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. 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
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
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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.
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.
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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.
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.
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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.
[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>.
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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
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