v6ops D. Wing
Internet-Draft A. Yourtchenko
Intended status: Standards Track Cisco
Expires: November 25, 2011 May 24, 2011
Happy Eyeballs: Trending Towards Success with Dual-Stack Hosts
draft-ietf-v6ops-happy-eyeballs-02
Abstract
This document describes an algorithm for a dual-stack client to
quickly determine the functioning address family to a dual-stack
server, and trend towards using that same address family for
subsequent connections. This improves the dual-stack user experience
during IPv6 or IPv4 server or network outages.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on November 25, 2011.
Copyright Notice
Copyright (c) 2011 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
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described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 4
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4
3.1. URIs and hostnames . . . . . . . . . . . . . . . . . . . . 4
3.2. IPv6 connectivity . . . . . . . . . . . . . . . . . . . . 5
4. Client Recommendations . . . . . . . . . . . . . . . . . . . . 5
5. Implementation details: A and AAAA . . . . . . . . . . . . . . 7
5.1. Description of State Variables . . . . . . . . . . . . . . 7
5.2. Initialization, Cache Flush, and Resetting Smoothed P . . 9
5.3. Connecting to a Server . . . . . . . . . . . . . . . . . . 9
5.4. Adjusting Address Family Preferences . . . . . . . . . . . 10
5.5. Exception Cache . . . . . . . . . . . . . . . . . . . . . 11
6. Implementation Details: SRV . . . . . . . . . . . . . . . . . 12
7. Additional Considerations . . . . . . . . . . . . . . . . . . 13
7.1. Additional Network and Host Traffic . . . . . . . . . . . 13
7.2. Abandon Non-Winning Connections . . . . . . . . . . . . . 13
7.3. Determining Address Type . . . . . . . . . . . . . . . . . 13
7.4. Debugging and Troubleshooting . . . . . . . . . . . . . . 13
7.5. DNS Behavior . . . . . . . . . . . . . . . . . . . . . . . 14
7.6. Middlebox Issues . . . . . . . . . . . . . . . . . . . . . 14
7.7. Multiple Interfaces . . . . . . . . . . . . . . . . . . . 14
7.8. Interaction with Same Origin Policy . . . . . . . . . . . 14
8. Content Provider Recommendations . . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 15
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
12.1. Normative References . . . . . . . . . . . . . . . . . . . 16
12.2. Informational References . . . . . . . . . . . . . . . . . 16
Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . . 17
A.1. changes from -01 to -02 . . . . . . . . . . . . . . . . . 18
A.2. changes from -00 to -01 . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
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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, a content provider may
ensure a positive user experience by using a DNS white list of IPv6
service providers who peer directly with them, e.g. [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.
This problem is also described in [RFC1671], published in 1994:
"The dual-stack code may get two addresses back from DNS; which
does it use? During the many years of transition the Internet
will contain black holes. For example, somewhere on the way from
IPng host A to IPng host B there will sometimes (unpredictably) be
IPv4-only routers which discard IPng packets. Also, the state of
the DNS does not necessarily correspond to reality. A host for
which DNS claims to know an IPng address may in fact not be
running IPng at a particular moment; thus an IPng packet to that
host will be discarded on delivery. Knowing that a host has both
IPv4 and IPng addresses gives no information about black holes. A
solution to this must be proposed and it must not depend on
manually maintained information. (If this is not solved, the dual
stack approach is no better than the packet translation
approach.)"
Even after the transition, the procedure described in this document
allows applications to strongly prefer IPv6 -- yet when an IPv6
outage occurs the application will quickly start using IPv4 and
continue using IPv4. It will quietly continue trying to use IPv6
until IPv6 becomes available again, and then trend again towards
using IPv6.
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.
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Applications would have to change in order to use the mechanism
described in this document, by either implementing the mechanism
directly, or by calling APIs made available to them. To improve IPv6
connectivity experience for legacy applications (e.g., applications
which simply rely on the operating system's address preference
order), operating systems may use other approaches. These can
include changing address sorting based on configuration received from
the network, other configuration, or dynamic detection of the host
connectivity to IPv6 and IPV4 destinations.
While the application recommendations in this document are described
in the context of HTTP clients ("web browsers") and SRV clients
(e.g., XMPP clients) the procedure is also useful and applicable to
other interactive applications.
Code which implements some of the ideas described in this document
has been made available [Perreault] [Andrews].
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
broken to specific prefixes or specific hosts, or slower than native
IPv4 connectivity.
3.1. URIs and hostnames
URIs are often used between users to exchange pointers to content --
such as on social networks, 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.
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3.2. IPv6 connectivity
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:db8::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.
Delays experienced by users of various browser and operating system
combinations have been studied [Experiences].
4. Client Recommendations
Happy Eyeballs does two things:
1. Provides fast connection for users. To provide fast connections
for users, 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 if it trended towards IPv4 Section 5.2.
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2. Avoids thrashing the network. Clients need to avoid flooding the
network or servers with excessive connection initiation traffic.
One way to accomplish this, without significant impairment to the
user experience, is to cache which address family has been
unsuccessful and successful, and use that address family for
subsequent connections to the same host.
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:db8::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 the 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).
After performing the above procedure, the client learns if
connections to the host's IPv6 or IPv4 address were successful. The
client MUST cache that information to avoid thrashing the network
with excessive subsequent connection attempts. For example, in the
diagram above, the client has noticed that IPv6 to that address
failed, and it should provide a greater preference to using IPv4
instead.
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DNS Server Client Server
| | |
1. |<--www.example.com A?-----| |
2. |<--www.example.com AAAA?--| |
3. |---192.0.2.1------------->| |
4. |---2001:db8::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
The diagram above shows a case where both IPv6 and IPv4 are working,
and IPv4 is abandoned (12).
5. Implementation details: A and AAAA
This section details how to provide robust dual stack service for
both IPv6 and IPv4, so that the user perceives very fast application
response.
Depending on implementation, the variables and procedures described
below might be implemented or maintained within a specific
application (e.g., web browser), library, framework, or by the
operating system itself. An API call such as "connect_by_name()" is
envisioned which would call the Happy Eyeballs routine and implement
the functions described in this section.
5.1. Description of State Variables
The system maintains a Smoothed P (which provides the overall
preference to IPv6 or IPv4), and an exception cache. Both of these
change over time and are described below:
Exception Cache: This is a cache, indexed by IP prefixes, contains
a "P" value for each prefix. Entries are added to this cache if a
connection to the expected address family failed and a connection
to the other address family succeeded. That is, these are
exceptions to the Smoothed P variable. See Section 5.5 for
description of how these prefixes are defined.
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(Note: In previous versions of this document, this was the
"per-destination P (preference) value".)
P: Address family preference. This is computed for this connection
attempt. A positive value is a preference to start the IPv6
connection first, a negative value to start the IPv4 connection
first, and zero indicates both IPv6 and IPv4 connections are
started simultaneously. The absolute value is the number of
milliseconds between the connection attempts on two address
families.
Smoothed P: Smoothed address family preference. This is the address
family preference for destinations that are not in the exception
cache. This variable can be positive or negative, with values
having the same meaning as "P". In the absence of more specific
configuration information, it is RECOMMENDED that implementations
enforce a maximum value of 8000 (8 seconds) for this variable.
(Note: In previous versions of this document, this was the
"application-wide P (preference) value".)
The following values are configured and constant:
TI: Tolerance Interval, in milliseconds. This is the allowance in
the time a connection is expected to complete and its actual
completion, and is provided to accommodate slight differences in
network and server responsiveness. In the absence of dynamic
configuration information from the network (e.g., DHCP) or other
configuration information, it is RECOMMENDED to use 20ms.
Initial Headstart (IH): The initial headstart ("preference") for
IPv6, in milliseconds. This value provides a preference towards
IPv6 (if positive) or IPv4 (if negative) when the host joins a new
network or otherwise flushes its cached information (see
Section 5.2), and the distance to move P away from zero when P was
zero. In the absence of dynamic configuration information from
the network (e.g., [I-D.ietf-6man-addr-select-opt]) or other
configuration information (e.g., the node's address selection
policy has been modified to prefer IPv4 over IPv6), the value
100ms is recommended, which causes the initial IPv6 connection to
be attempted 100ms before the IPv4 connection.
MAXWAIT: Maximum wait time for a connection to complete, before
trying additional IP addresses. This is RECOMMENDED to be 10
seconds.
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5.2. Initialization, Cache Flush, and Resetting Smoothed P
Because every network has different characteristics (e.g., working or
broken IPv6 or IPv4 connectivity) the Smoothed P variable SHOULD be
set to its default value (Smoothed P = Initial Headstart) and the
exception cache SHOULD be emptied whenever the host is connected to a
new network (e.g., DNAv4 [RFC4436], DNAv6 [RFC6059], [cx-osx],
[cx-win]).
If there are IPv6 failures to specific hosts or prefixes, the
exception cache will build up exception entries preferring IPv4, and
if there are significant IPv6 failures to many hosts or prefixes,
Smoothed P will become negative. When this occurs, IPv6 will not be
attempted at all. To avoid this problem, it is strongly RECOMMENDED
to occasionally flush the exception cache of all entries and reset
Smoothed P to Initial Offset. This SHOULD be done every 10 minutes.
In so doing, IPv6 and IPv4 are tried again so that if the IPv6 is
working again, it will quickly be preferred again.
5.3. Connecting to a Server
The steps when connecting to a server are as follows:
1. query DNS using getaddrinfo(). This will return addresses sorted
by the host's default address selection ordering [RFC3484], its
updates, or the address selection as chosen by the network
administrator [I-D.ietf-6man-addr-select-opt].
2. If this returns both an IPv6 and IPv4 address, continue
processing to the next stop. Otherwise, Happy Eyeballs
processing stops here.
3. Of the addresses returned in step (1), look up the first IPv6
address and first IPv4 address in the Happy Eyeballs exception
cache. Matching entries in the exception cache influence the P
value for this connection attempt by setting P to the sum of
Smoothed_P and of the P values from the matching IPv6 entry (if
it exists) and the matching IPv4 entry (if it exists).
4. If P>=0, initiate a connection attempt using the first IPv6
address returned by step (1). If that connection has not
completed after P milliseconds, initiate a connection attempt
using IPv4.
5. If P<=0, initiate a connection attempt using the first IPv4
address returned by getaddrinfo. If that connection has not
completed after absolute value(P) milliseconds, initiate a
connection attempt using IPv6.
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6. If neither connection has completed after MAXWAIT seconds, repeat
the procedure at step (3) until the addresses are exhausted.
After performing the above steps, there will be no connection at all
or one connection will complete first. If no connection was
successful, it should be treated as a failure for both IPv6 and IPv4.
5.4. Adjusting Address Family Preferences
If the preferred address family completed first, Smoothed P is
adjusted towards that address family. If the non-preferred address
family completed, we wait an additional Tolerance Interval
milliseconds for the preferred address family to complete. If the
expected address family succeeded, we increment the absolute value of
the Smoothed P; if the expected address family failed - we create an
exception entry that will make an adjustment to the future value of P
for the attempt on this pair in the direction opposite to the current
sign of Smoothed P.
The table below summarizes the adjustments:
| Connection completed within Tolerance Interval |
+--------+--------------|------------------|------------------+
| | v6 and v4 ok | v6 ok, v4 failed | v6 failed, v4 ok |
+--------+--------------|------------------|------------------+
| P > 0 | SP=SP+10 | SP=SP+10 | SP=SP/2 or cache |
| P < 0 | SP=SP+10 | SP=SP/2 or cache | SP=SP-10 |
| P = 0 |SP=big(10,IH) | SP=IH | SP=(-IH) |
|--------+--------------|------------------|------------------+
Figure 4: Table summarizing P adjustments
The the above table is described in textual form:
o If P > 0 (indicating IPv6 is preferred over IPv4):
* and both the IPv6 and IPv4 connection attempts completed within
the Tolerance Interval, it means the IPv6 preference was
accurate or we should gently prefer IPv6, so Smoothed P is
increased by 10 milliseconds (Smoothed P = Smoothed P + 10).
* If the IPv6 connection completed but the IPv4 connection failed
within the tolerance interval, it means future connections
should prefer IPv6, so Smoothed P is increased by 10
milliseconds (Smoothed_P = Smoothed_P + 10).
* If the IPv6 connection failed but the IPv4 connection completed
within the tolerance interval, it means the IPv6 preference is
inaccurate. If no exception cache entry exists for the IPv6
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and IPv4 prefixes, the entries are created and their P value
set to to the connection setup time * -1, and Smoothed P is
halved and rounded towards zero (Smoothed_P = Smoothed_P *
0.5). If an exception cache entry already existed, its P value
is doubled and Smoothed_P is not adjusted.
o If P < 0 (indicating IPv4 is preferred over IPv6):
* and both the IPv6 and IPv4 connection attempts completed within
the tolerance interval, we should gently prefer IPv6, so
Smoothed P is increased by 10 milliseconds (Smoothed_P =
Smoothed_P + 10).
* If the IPv6 connection completed but the IPv4 connection failed
within within the tolerance interval, it means the IPv4
preference is inaccurate. If no exception cache entry exists
for the IPv6 and IPv4 prefixes, they are created and their P
values set to the connection setup time and Smoothed P is
halved and rounded towards 0 (Smoothed_P = Smoothed_P * 0.5).
If an exception cahe entry already existed, its P value is
doubled and Smoothed_P is not adjusted.
* If the IPv4 connection completed but the IPv6 connection failed
within the tolerance interval, it means future connections
should prefer IPv4, so Smoothed P is decreased by 10
milliseconds (Smoothed_P = Smoothed_P - 10).
o If P = 0 (indicating IPv4 and IPv6 are equally preferred):
* and both the IPv6 and IPv4 connection attempts completed within
the tolerance interval, we should prefer IPv6 significantly, so
Smoothed P is set to the larger of Initial Headstart or 10
(Smoothed_P = larger(Initial Headstart, 10)).
* if the IPv6 connection completed but the IPv4 connection failed
within the Tolerance Interval, it means we need to prefer IPv6,
so Smoothed P is increased by 10 (Smoothed_P = Smoothed_P +
10).
* if the IPv4 connection completed but the IPv6 connection failed
within the Tolerance Interval, it means we need to prefer IPv4,
so P is decreased by 10 (Smoothed_P = Smoothed_P - 10).
5.5. Exception Cache
An exception cache is maintained of IPv6 prefixes and IPv4 prefixes,
which are exceptions to the Smoothed P value at the time a connection
was made. For IPv6 prefixes, the default prefix length is 64. For
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IPv4, the default prefix length is /32.
The exception cache MAY be a fixed size, removing entires using a
least-frequently used algorithm. This works because the network path
is likely to change over time (thus old entries aren't valuable
anyway), and if an entry does not exist the Smoothed P value will
still provide some avoidance of user-noticable connection setup
delay.
6. Implementation Details: SRV
[[Editor's Note: SRV processing needs to be incorporated into the
above section, rather than described separately. This will be
done in a future update to this document.]]
For the purposes of this section, "client" is defined as the entity
initiating the connection.
For protocols which support DNS SRV [RFC2782], the client performs
the IN SRV query (e.g. IN SRV _xmpp-client._tcp.example.com) as
normal. The client MUST perform the following steps:
1. Sort all SRV records according to priority (lowest priority
first)
2. Process all of the SRV targets of the same priority with a weight
greater than 0:
A. Perform A/AAAA queries for each SRV target in parallel, as
described in the A/AAAA processing section
B. Connect to the IPv4/IPv6 addresses
C. If at least one connection succeeds, stop processing SRV
records
3. If there is no connection, process all of the SRV targets of the
same priority with a weight of 0, as per steps 2.1 through 2.3
above
4. Repeat steps 2.1 through 2.3 for the next priority, until a
connection is established or all SRV records have been exhausted
5. If there is still no connection, fallback to using the domain
(e.g., example.com), following steps 2.1 through 2.3 above
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7. Additional Considerations
This section discusses considerations and requirements that are
common to new technology deployment.
7.1. Additional Network and Host Traffic
Additional network traffic and additional server load is created due
to the recommendations in this document. This additional load is
mitigated by the P value, especially the exception cache P value.
The procedures described in this document retain a quality user
experience while transitioning from IPv4-only to dual stack, while
still giving IPv6 a slight preference over IPv4 (in order to remove
load from IPv4 networks, most importantly to reduce the load on IPv4
network address translators). The improvement in the user experience
benefits the user to only a small detriment of the network, DNS
server, and server that are serving the user.
7.2. Abandon Non-Winning Connections
It is RECOMMENDED that the non-winning connections be abandoned, even
though they could -- in some cases -- be put to reasonable use. To
take HTTP as an example, the design of some sites can break because
of HTTP cookies that incorporate the client's IP address, require all
connections be from the same IP address. If some connections from
the same client are arriving from different IP addresses, such
applications will break. It is also important to abandon connections
to avoid consuming server resources (file descriptors, TCP control
blocks) or middlebox resources (e.g., NAPT). Using the non-winning
connection can also interfere with the browser's Same Origin Policy
(see Section 7.8).
7.3. Determining Address Type
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). While IPv6/IPv4 translation makes that difficult,
fortunately IPv6/IPv4 translators are not deployed on networks with
dual stack clients, which is the scope of this document.
7.4. Debugging and Troubleshooting
This mechanism 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 any
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particular transport. To assist in that regard, the applications
implementing the proposal in this document SHOULD also provide a
mechanism to revert the behavior to that of a default provided by the
operating system - the [RFC3484].
7.5. 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 03: It is believed these defective DNS servers
have long since been upgraded. If so, we can remove this
section.]]
7.6. 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 middlebox issue is
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 from the
same port.
For the large part, these issues with simultaneous DNS requests are
believed to be fixed.
7.7. Multiple Interfaces
Interaction of the suggestions in this document with multiple
interfaces, and interaction with the MIF working group, is for
further study ([I-D.chen-mif-happy-eyeballs-extension] is devoted to
this).
7.8. Interaction with Same Origin Policy
Web browsers implement same origin policy (SOP, [sop],
[I-D.abarth-origin]), which causes subsequent connections to the same
hostname to go to the same IPv4 (or IPv6) address as the previous
successful connection. This is done to prevent certain types of
attacks.
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The same-origin policy harms user-visible responsiveness if a new
connection fails (e.g., due to a transient event such as router
failure or load balancer failure). While it is tempting to use Happy
Eyeballs to maintain responsiveness, web browsers MUST NOT change
their same origin policy because of Happy Eyeballs
8. Content Provider Recommendations
Content providers SHOULD provide both AAAA and A records for servers
using the same DNS name for both IPv4 and IPv6.
9. Security Considerations
[[Placeholder.]]
See Section 7.2 and Section 7.8.
10. 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, Rick Jones, Stig Venaas, Erik Kline, Bjoern
Zeeb, Matt Miller, Dave Thaler, and Dmitry Anipko for providing
feedback on the document.
Thanks to Javier Ubillos, Simon Perreault and Mark Andrews for the
active feedback and the experimental work on the independent
practical implementations that they created.
Also the authors would like to thank the following individuals who
participated in various email discussions on this topic: Mohacsi
Janos, Pekka Savola, Ted Lemon, Carlos Martinez-Cagnazzo, Simon
Perreault, Jack Bates, Jeroen Massar, Fred Baker, Javier Ubillos,
Teemu Savolainen, Scott Brim, Erik Kline, Cameron Byrne, Daniel
Roesen, Guillaume Leclanche, Mark Smith, Gert Doering, Martin
Millnert, Tim Durack, Matthew Palmer.
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11. IANA Considerations
This document has no IANA actions.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
12.2. Informational References
[Andrews] Andrews, M., "How to connect to a multi-homed server over
TCP", January 2011, <http://www.isc.org/community/blog/
201101/how-to-connect-to-a-multi-h omed-server-over-tcp>.
[DNS-middlebox]
Various, "DNS middlebox behavior with multiple queries
over same source port", June 2009,
<https://bugzilla.redhat.com/show_bug.cgi?id=505105>.
[Experiences]
Savolainen, T., Miettinen, N., Veikkolainen, S., Chown,
T., and J. Morse, "Experiences of host behavior in broken
IPv6 networks", March 2011,
<http://www.ietf.org/proceedings/80/slides/v6ops-12.pdf>.
[I-D.abarth-origin]
Barth, A., "The Web Origin Concept",
draft-abarth-origin-09 (work in progress), November 2010.
[I-D.chen-mif-happy-eyeballs-extension]
Chen, G. and C. Williams, "Happy Eyeballs Extension for
Multiple Interfaces",
draft-chen-mif-happy-eyeballs-extension-01 (work in
progress), March 2011.
[I-D.ietf-6man-addr-select-opt]
Matsumoto, A., Fujisaki, T., and J. Kato, "Distributing
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Address Selection Policy using DHCPv6",
draft-ietf-6man-addr-select-opt-00 (work in progress),
December 2010.
[Perreault]
Perreault, S., "Happy Eyeballs in Erlang", February 2011,
<http://www.viagenie.ca/news/
index.html#happy_eyeballs_erlang>.
[RFC1671] Carpenter, B., "IPng White Paper on Transition and Other
Considerations", RFC 1671, August 1994.
[RFC4074] Morishita, Y. and T. Jinmei, "Common Misbehavior Against
DNS Queries for IPv6 Addresses", RFC 4074, May 2005.
[RFC4436] Aboba, B., Carlson, J., and S. Cheshire, "Detecting
Network Attachment in IPv4 (DNAv4)", RFC 4436, March 2006.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
April 2010.
[RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for
Detecting Network Attachment in IPv6", RFC 6059,
November 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>.
[sop] W3C, "Same Origin Policy", January 2010,
<http://www.w3.org/Security/wiki/Same_Origin_Policy>.
[whitelist]
Google, "Google IPv6 DNS Whitelist", January 2009,
<http://www.google.com/intl/en/ipv6>.
Appendix A. Changes
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A.1. changes from -01 to -02
o Now honors host's address preference (RFC3484 and friends)
o No longer requires thread-safe DNS library. It uses getaddrinfo()
o No longer describes threading.
o IPv6 is given a 200ms head start (Initial Headstart variable).
o If the IPv6 and IPv4 connection attempts were made at nearly the
same time, wait Tolerance Interval milliseconds for both to
complete before deciding which one wins.
o Renamed "global P" to "Smoothed P", and better described how it is
calculated.
o introduced the exception cache. This contains the set of networks
that only work with IPv4 (or only with IPv6), so that subsequent
connection attempts use that address family without them causing
serious affect to Smoothed P.
o encourages that every 10 minutes the exception cache and Smoothed
P be reset. This allows IPv6 to be attempted again, so we don't
get 'stuck' on IPv4.
o If we didn't get both A and AAAA, abandon all Happy Eyeballs
processing (thanks to Simon Perreault).
o added discussion of Same Origin Policy
o Removed discussion of NAT-PT and address learning; those are only
used with IPv6-only hosts whereas this document is about dual-
stack hosts contacting dual-stack servers.
A.2. changes from -00 to -01
o added SRV section (thanks to Matt Miller)
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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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