draft-ietf-v6ops-happy-eyeballs-02.txt   draft-ietf-v6ops-happy-eyeballs-03.txt 
v6ops D. Wing v6ops D. Wing
Internet-Draft A. Yourtchenko Internet-Draft A. Yourtchenko
Intended status: Standards Track Cisco Intended status: Standards Track Cisco
Expires: November 25, 2011 May 24, 2011 Expires: January 9, 2012 July 8, 2011
Happy Eyeballs: Trending Towards Success with Dual-Stack Hosts Happy Eyeballs: Success with Dual-Stack Hosts
draft-ietf-v6ops-happy-eyeballs-02 draft-ietf-v6ops-happy-eyeballs-03
Abstract Abstract
This document describes an algorithm for a dual-stack client to When the IPv4 server and path is working but the IPv6 server or IPv6
quickly determine the functioning address family to a dual-stack path is down, a dual-stack client application experiences significant
server, and trend towards using that same address family for connection delay compared to an IPv4-only client. This is
subsequent connections. This improves the dual-stack user experience undesirable because it causes the dual-stack client to have a worse
during IPv6 or IPv4 server or network outages. user experience. This document specifies requirements for algorithms
that reduce this delay, and provides an example algorithm.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 25, 2011. This Internet-Draft will expire on January 9, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 4 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
3.1. URIs and hostnames . . . . . . . . . . . . . . . . . . . . 4 3.1. URIs and hostnames . . . . . . . . . . . . . . . . . . . . 4
3.2. IPv6 connectivity . . . . . . . . . . . . . . . . . . . . 5 3.2. IPv6 connectivity . . . . . . . . . . . . . . . . . . . . 4
4. Client Recommendations . . . . . . . . . . . . . . . . . . . . 5 4. Algorithm Requirements . . . . . . . . . . . . . . . . . . . . 5
5. Implementation details: A and AAAA . . . . . . . . . . . . . . 7 4.1. Adhere to Address Preference Policy . . . . . . . . . . . 6
5.1. Description of State Variables . . . . . . . . . . . . . . 7 4.2. Behavior when Preferred Address Family has Failed . . . . 7
5.2. Initialization, Cache Flush, and Resetting Smoothed P . . 9 4.3. Reset on Network (re-)Initialization . . . . . . . . . . . 7
5.3. Connecting to a Server . . . . . . . . . . . . . . . . . . 9 4.4. Abandon Non-Winning Connections . . . . . . . . . . . . . 7
5.4. Adjusting Address Family Preferences . . . . . . . . . . . 10 5. Additional Considerations . . . . . . . . . . . . . . . . . . 8
5.5. Exception Cache . . . . . . . . . . . . . . . . . . . . . 11 5.1. Additional Network and Host Traffic . . . . . . . . . . . 8
6. Implementation Details: SRV . . . . . . . . . . . . . . . . . 12 5.2. Determining Address Type . . . . . . . . . . . . . . . . . 8
7. Additional Considerations . . . . . . . . . . . . . . . . . . 13 5.3. Debugging and Troubleshooting . . . . . . . . . . . . . . 8
7.1. Additional Network and Host Traffic . . . . . . . . . . . 13 5.4. Multiple Interfaces . . . . . . . . . . . . . . . . . . . 9
7.2. Abandon Non-Winning Connections . . . . . . . . . . . . . 13 5.5. Interaction with Same Origin Policy . . . . . . . . . . . 9
7.3. Determining Address Type . . . . . . . . . . . . . . . . . 13 5.6. Happy Eyeballs in an Operating System . . . . . . . . . . 9
7.4. Debugging and Troubleshooting . . . . . . . . . . . . . . 13 6. Example Algorithm . . . . . . . . . . . . . . . . . . . . . . 9
7.5. DNS Behavior . . . . . . . . . . . . . . . . . . . . . . . 14 7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7.6. Middlebox Issues . . . . . . . . . . . . . . . . . . . . . 14 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
7.7. Multiple Interfaces . . . . . . . . . . . . . . . . . . . 14 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7.8. Interaction with Same Origin Policy . . . . . . . . . . . 14 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8. Content Provider Recommendations . . . . . . . . . . . . . . . 15 10.1. Normative References . . . . . . . . . . . . . . . . . . . 11
9. Security Considerations . . . . . . . . . . . . . . . . . . . 15 10.2. Informational References . . . . . . . . . . . . . . . . . 11
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15 Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . . 12
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 A.1. changes from -02 to -03 . . . . . . . . . . . . . . . . . 12
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 A.2. changes from -01 to -02 . . . . . . . . . . . . . . . . . 12
12.1. Normative References . . . . . . . . . . . . . . . . . . . 16 A.3. changes from -00 to -01 . . . . . . . . . . . . . . . . . 13
12.2. Informational References . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . . 17
A.1. changes from -01 to -02 . . . . . . . . . . . . . . . . . 18
A.2. changes from -00 to -01 . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction 1. Introduction
In order to use HTTP successfully over IPv6, it is necessary that the In order to use applications over IPv6, it is necessary that users
user enjoys nearly identical performance as compared to IPv4. A enjoy nearly identical performance as compared to IPv4. A
combination of today's applications, IPv6 tunneling and IPv6 service combination of today's applications, IPv6 tunneling, IPv6 service
providers, and some of today's content providers all cause the user providers, and some of today's content providers all cause the user
experience to suffer (Section 3). For IPv6, a content provider may experience to suffer (Section 3). For IPv6, a content provider may
ensure a positive user experience by using a DNS white list of IPv6 ensure a positive user experience by using a DNS white list of IPv6
service providers who peer directly with them, e.g. [whitelist]. service providers who peer directly with them (e.g., [whitelist]).
However, this is not scalable to all service providers worldwide, nor However, this does not scale well (to the number of DNS servers
is it scalable for other content providers to operate their own DNS worldwide or the number of content providers worldwide), and does not
white list. react to intermittent network path outages.
Instead, this document suggests a mechanism for applications to Instead, applications can improve the user experience themselves, by
quickly determine if IPv6 or IPv4 is the most optimal to connect to a more aggressively making connections on IPv6 and IPv4. There are a
server. The suggestions in this document provide a user experience variety of algorithms that can be envisioned. This document
which is superior to connecting to ordered IP addresses which is specifies requirements for any such algorithm, with the goals that
helpful during the IPv6/IPv4 transition with dual stack hosts. the network and servers are not inordinately harmed with a simple
doubling of traffic on IPv6 and IPv4, and the host's address
preference is honored (e.g., [RFC3484]).
This problem is also described in [RFC1671], published in 1994: 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
The basis of the IPv6/IPv4 selection problem was first described in
1994 in [RFC1671],
"The dual-stack code may get two addresses back from DNS; which "The dual-stack code may get two addresses back from DNS; which
does it use? During the many years of transition the Internet does it use? During the many years of transition the Internet
will contain black holes. For example, somewhere on the way from will contain black holes. For example, somewhere on the way from
IPng host A to IPng host B there will sometimes (unpredictably) be IPng host A to IPng host B there will sometimes (unpredictably) be
IPv4-only routers which discard IPng packets. Also, the state of IPv4-only routers which discard IPng packets. Also, the state of
the DNS does not necessarily correspond to reality. A host for the DNS does not necessarily correspond to reality. A host for
which DNS claims to know an IPng address may in fact not be 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 running IPng at a particular moment; thus an IPng packet to that
host will be discarded on delivery. Knowing that a host has both host will be discarded on delivery. Knowing that a host has both
IPv4 and IPng addresses gives no information about black holes. A IPv4 and IPng addresses gives no information about black holes. A
solution to this must be proposed and it must not depend on solution to this must be proposed and it must not depend on
manually maintained information. (If this is not solved, the dual manually maintained information. (If this is not solved, the dual
stack approach is no better than the packet translation stack approach is no better than the packet translation
approach.)" 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.
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 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 same URI and hostname be used for IPv4 and IPv6. Using separate
namespaces causes namespace fragmentation and reduces the ability for namespaces (e.g., "ipv6.example.com") causes namespace fragmentation
users to share URIs and hostnames, and complicates printed material and reduces the ability for users to share URIs and hostnames, and
that includes the URI or hostname. complicates printed material that includes the URI or hostname.
As discussed in more detail in Section 3.2, IPv6 connectivity is As discussed in more detail in Section 3.2, IPv6 connectivity is
broken to specific prefixes or specific hosts, or slower than native broken to specific prefixes or specific hosts, or slower than native
IPv4 connectivity. IPv4 connectivity.
3.1. URIs and hostnames 3.1. URIs and hostnames
URIs are often used between users to exchange pointers to content -- URIs are often used between users to exchange pointers to content --
such as on social networks, email, instant messaging, or other such as on social networks, email, instant messaging, or other
systems. Thus, production URIs and production hostnames containing systems. Thus, production URIs and production hostnames containing
skipping to change at page 5, line 34 skipping to change at page 5, line 4
7. | |--TCP SYN, IPv6--->X | 7. | |--TCP SYN, IPv6--->X |
8. | |--TCP SYN, IPv6--->X | 8. | |--TCP SYN, IPv6--->X |
9. | | | 9. | | |
10. | |--TCP SYN, IPv4------->| 10. | |--TCP SYN, IPv4------->|
11. | |<-TCP SYN+ACK, IPv4----| 11. | |<-TCP SYN+ACK, IPv4----|
12. | |--TCP ACK, IPv4------->| 12. | |--TCP ACK, IPv4------->|
Figure 1: Existing behavior message flow Figure 1: Existing behavior message flow
The client obtains the IPv4 and IPv6 records for the server (1-4). 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 The client attempts to connect using IPv6 to the server, but the IPv6
path is broken (6-8), which consumes several seconds of time. path is broken (6-8), which consumes several seconds of time.
Eventually, the client attempts to connect using IPv4 (10) which Eventually, the client attempts to connect using IPv4 (10) which
succeeds. succeeds.
Delays experienced by users of various browser and operating system Delays experienced by users of various browser and operating system
combinations have been studied [Experiences]. combinations have been studied [Experiences].
4. Client Recommendations 4. Algorithm Requirements
Happy Eyeballs does two things: A Happy Eyeballs algorithm has two primary goals:
1. Provides fast connection for users. To provide fast connections 1. Provides fast connection for users, by quickly attempting to
for users, clients should make connections quickly over various connect using IPv6 and IPv4.
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.
2. Avoids thrashing the network. Clients need to avoid flooding the 2. Avoids thrashing the network, by not always making simultaneous
network or servers with excessive connection initiation traffic. IPv6 and IPv4 connection attempts.
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 The basic idea is depicted in the following diagram:
IPv6 networks, it can perform the procedures described in this
section.
DNS Server Client Server DNS Server Client Server
| | | | | |
1. |<--www.example.com A?-----| | 1. |<--www.example.com A?-----| |
2. |<--www.example.com AAAA?--| | 2. |<--www.example.com AAAA?--| |
3. |---192.0.2.1------------->| | 3. |---192.0.2.1------------->| |
4. |---2001:db8::1----------->| | 4. |---2001:db8::1----------->| |
5. | | | 5. | | |
6. | |==TCP SYN, IPv6===>X | 6. | |==TCP SYN, IPv6===>X |
7. | |--TCP SYN, IPv4------->| 7. | |--TCP SYN, IPv4------->|
skipping to change at page 7, line 25 skipping to change at page 6, line 26
9. | |<-TCP SYN+ACK, IPv4----| 9. | |<-TCP SYN+ACK, IPv4----|
10. | |==TCP ACK, IPv6=======>| 10. | |==TCP ACK, IPv6=======>|
11. | |--TCP ACK, IPv4------->| 11. | |--TCP ACK, IPv4------->|
12. | |--TCP RST, IPv4------->| 12. | |--TCP RST, IPv4------->|
Figure 3: Happy Eyeballs flow 2, IPv6 working Figure 3: Happy Eyeballs flow 2, IPv6 working
The diagram above shows a case where both IPv6 and IPv4 are working, The diagram above shows a case where both IPv6 and IPv4 are working,
and IPv4 is abandoned (12). and IPv4 is abandoned (12).
5. Implementation details: A and AAAA Any Happy Eyeballs algorithm will persist in products for as long as
the client host is dual-stacked, which will persist as long as there
This section details how to provide robust dual stack service for are IPv4-only servers on the Internet -- the so-called "long tail".
both IPv6 and IPv4, so that the user perceives very fast application Over time, as most content is available via IPv6, the amount of IPv4
response. traffic will decrease. This means that the IPv4 infrastructure will,
over time, be sized to accomodate that decreased (and decreasing)
Depending on implementation, the variables and procedures described amount of traffic. It is critical that a Happy Eyeballs algorithm
below might be implemented or maintained within a specific not cause a surge of unnecessary traffic on that IPv4 infrastructure.
application (e.g., web browser), library, framework, or by the To meet that goal, compliant Happy Eyeballs algorithms must adhere to
operating system itself. An API call such as "connect_by_name()" is the requirements in this section.
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.
(Note: In previous versions of this document, this was the 4.1. Adhere to Address Preference Policy
"per-destination P (preference) value".)
P: Address family preference. This is computed for this connection All hosts have an address selection policy. IPv6-capable hosts
attempt. A positive value is a preference to start the IPv6 usually implement [RFC3484] and may allow the user (via configuration
connection first, a negative value to start the IPv4 connection commands) or the network to modify that address selection policy
first, and zero indicates both IPv6 and IPv4 connections are (e.g., [I-D.ietf-6man-addr-select-opt]). In most cases, the
started simultaneously. The absolute value is the number of preferred address family is IPv6.
milliseconds between the connection attempts on two address
families.
Smoothed P: Smoothed address family preference. This is the address Happy Eyeballs implementations MUST follow the host's address
family preference for destinations that are not in the exception preference policy or, if that policy is unknown, implementations MUST
cache. This variable can be positive or negative, with values prefer IPv6 over IPv4.
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 Justification: This reduces load on stateful IPv4 middleboxes
"application-wide P (preference) value".) (NAT and firewalls) and reduces IPv4 address sharing contention.
The following values are configured and constant: 4.2. Behavior when Preferred Address Family has Failed
TI: Tolerance Interval, in milliseconds. This is the allowance in After making a connection attempt on a certain address family (e.g.,
the time a connection is expected to complete and its actual IPv6), a Happy Eyeballs implementation will decide to initiate a
completion, and is provided to accommodate slight differences in second connection attempt using the other address family (e.g.,
network and server responsiveness. In the absence of dynamic IPv4).
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 After doing so and noticing that connections using the other address
IPv6, in milliseconds. This value provides a preference towards family (e.g., IPv4) are successful, a Happy Eyeballs implementation
IPv6 (if positive) or IPv4 (if negative) when the host joins a new MAY make subsequent connection attempts on the successful address
network or otherwise flushes its cached information (see family (e.g., IPv4). Such an implementationMUST occasionally make
Section 5.2), and the distance to move P away from zero when P was connection attempts using the host's preferred address family, as it
zero. In the absence of dynamic configuration information from may have become functional. It is RECOMMENDED that implementations
the network (e.g., [I-D.ietf-6man-addr-select-opt]) or other try the preferred address family at least every 10 minutes. Note:
configuration information (e.g., the node's address selection this can be achieved by connecting to both address families at the
policy has been modified to prefer IPv4 over IPv6), the value same time, which does not significantly harm the application's
100ms is recommended, which causes the initial IPv6 connection to connection setup time for the successful address family. If
be attempted 100ms before the IPv4 connection. connections using the preferred address family are successful, the
preferred address family SHOULD be used for subsequent connections.
MAXWAIT: Maximum wait time for a connection to complete, before Justification: Once the IPv6 path becomes usable again, this
trying additional IP addresses. This is RECOMMENDED to be 10 reduces load on stateful IPv4 middleboxes (NAT and firewalls) and
seconds. reduces IPv4 address sharing contention.
5.2. Initialization, Cache Flush, and Resetting Smoothed P 4.3. Reset on Network (re-)Initialization
Because every network has different characteristics (e.g., working or Because every network has different characteristics (e.g., working or
broken IPv6 or IPv4 connectivity) the Smoothed P variable SHOULD be broken IPv6 or IPv4 connectivity), a Happy Eyeballs algorithm SHOULD
set to its default value (Smoothed P = Initial Headstart) and the re-initialize when the host is connected to a new network. Hosts can
exception cache SHOULD be emptied whenever the host is connected to a determine network (re-)initialization by a variety of mechanisms
new network (e.g., DNAv4 [RFC4436], DNAv6 [RFC6059], [cx-osx], including DNAv4 [RFC4436], DNAv6 [RFC6059], [cx-osx], [cx-win].
[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.
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
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
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 Justification: This provides the best chance that IPv6 will be
described in the A/AAAA processing section attempted over the new interface.
B. Connect to the IPv4/IPv6 addresses If the client application is a web browser, see also Section 5.5.
C. If at least one connection succeeds, stop processing SRV 4.4. Abandon Non-Winning Connections
records
3. If there is no connection, process all of the SRV targets of the It is RECOMMENDED that the non-winning connections be abandoned, even
same priority with a weight of 0, as per steps 2.1 through 2.3 though they could -- in some cases -- be put to reasonable use.
above
4. Repeat steps 2.1 through 2.3 for the next priority, until a Justification: This reduces the load on the server (file
connection is established or all SRV records have been exhausted descriptors, TCP control blocks), stateful middleboxes (NAT and
firewalls) and, if the abandoned connection is IPv4, reduces IPv4
address sharing contention.
5. If there is still no connection, fallback to using the domain HTTP: The design of some sites can break because of HTTP cookies
(e.g., example.com), following steps 2.1 through 2.3 above that incorporate the client's IP address and require all
connections be from the same IP address. If some connections from
the same client are arriving from different IP addresses (or
worse, different IP address families), such applications will
break. Additionally for HTTP, using the non-winning connection
can interfere with the browser's Same Origin Policy (see
Section 5.5).
7. Additional Considerations 5. Additional Considerations
This section discusses considerations and requirements that are This section discusses considerations and requirements that are
common to new technology deployment. common to new technology deployment.
7.1. Additional Network and Host Traffic 5.1. Additional Network and Host Traffic
Additional network traffic and additional server load is created due Additional network traffic and additional server load is created due
to the recommendations in this document. This additional load is to the recommendations in this document, especially when connections
mitigated by the P value, especially the exception cache P value. to the perferred address family (usually IPv6) are not completing
quickly.
The procedures described in this document retain a quality user The procedures described in this document retain a quality user
experience while transitioning from IPv4-only to dual stack, while experience while transitioning from IPv4-only to dual stack, while
still giving IPv6 a slight preference over IPv4 (in order to remove still giving IPv6 a slight preference over IPv4 (in order to remove
load from IPv4 networks, most importantly to reduce the load on IPv4 load from IPv4 networks, most importantly to reduce the load on IPv4
network address translators). The improvement in the user experience network address translators). The improvement in the user experience
benefits the user to only a small detriment of the network, DNS benefits the user to only a small detriment of the network, DNS
server, and server that are serving the user. server, and server that are serving the user.
7.2. Abandon Non-Winning Connections 5.2. Determining Address Type
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 For some transitional technologies such as a dual-stack host, it is
easy for the application to recognize the native IPv6 address easy for the application to recognize the native IPv6 address
(learned via a AAAA query) and the native IPv4 address (learned via (learned via a AAAA query) and the native IPv4 address (learned via
an A query). While IPv6/IPv4 translation makes that difficult, an A query). While IPv6/IPv4 translation makes that difficult,
fortunately IPv6/IPv4 translators are not deployed on networks with fortunately IPv6/IPv4 translators are not deployed on networks with
dual stack clients, which is the scope of this document. dual stack clients.
7.4. Debugging and Troubleshooting 5.3. Debugging and Troubleshooting
This mechanism is aimed at ensuring a reliable user experience This mechanism is aimed at ensuring a reliable user experience
regardless of connectivity problems affecting any single transport. regardless of connectivity problems affecting any single transport.
However, this naturally means that applications employing these However, this naturally means that applications employing these
techniques are by default less useful for diagnosing issues with any techniques are by default less useful for diagnosing issues with a
particular transport. To assist in that regard, the applications particular address family. To assist in that regard, the
implementing the proposal in this document SHOULD also provide a implementions MAY also provide a mechanism to disable their Happy
mechanism to revert the behavior to that of a default provided by the Eyeballs behavior via a user setting.
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 5.4. Multiple Interfaces
Interaction of the suggestions in this document with multiple Interaction of the suggestions in this document with multiple
interfaces, and interaction with the MIF working group, is for interfaces, and interaction with the MIF working group, is for
further study ([I-D.chen-mif-happy-eyeballs-extension] is devoted to further study.
this).
7.8. Interaction with Same Origin Policy 5.5. Interaction with Same Origin Policy
Web browsers implement same origin policy (SOP, [sop], Web browsers implement same origin policy (SOP, [sop],
[I-D.abarth-origin]), which causes subsequent connections to the same [I-D.abarth-origin]), which causes subsequent connections to the same
hostname to go to the same IPv4 (or IPv6) address as the previous hostname to go to the same IPv4 (or IPv6) address as the previous
successful connection. This is done to prevent certain types of successful connection. This is done to prevent certain types of
attacks. attacks.
The same-origin policy harms user-visible responsiveness if a new The same-origin policy harms user-visible responsiveness if a new
connection fails (e.g., due to a transient event such as router connection fails (e.g., due to a transient event such as router
failure or load balancer failure). While it is tempting to use Happy failure or load balancer failure). While it is tempting to use Happy
Eyeballs to maintain responsiveness, web browsers MUST NOT change Eyeballs to maintain responsiveness, web browsers MUST NOT change
their same origin policy because of Happy Eyeballs their same origin policy because of Happy Eyeballs
8. Content Provider Recommendations 5.6. Happy Eyeballs in an Operating System
Content providers SHOULD provide both AAAA and A records for servers Applications would have to change in order to use the mechanism
using the same DNS name for both IPv4 and IPv6. 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 consider more sophisticated approaches.
These can include changing address sorting based on configuration
received from the network, or observing connection failures to IPv6
and IPV4 destinations.
9. Security Considerations 6. Example Algorithm
[[Placeholder.]] What follows is the algorithm implemented in Google Chrome and
Mozilla Firefox.
See Section 7.2 and Section 7.8. 1. Call getaddinfo(), which returns a list of IP addresses sorted by
the host's address preference policy.
10. Acknowledgements 2. Initiate a connection attempt with the first address in that list
(e.g., IPv6).
3. If that connection does not complete within a short period of
time (e.g., 200-300ms), initiate a connection attempt with the
first address belonging to the other address family (e.g., IPv4)
4. The first connection that is established is used. The other
connection is discarded.
Other example algorithms include [Perreault] and [Andrews].
7. Security Considerations
See Section 4.4 and Section 5.5.
8. Acknowledgements
The mechanism described in this paper was inspired by Stuart The mechanism described in this paper was inspired by Stuart
Cheshire's discussion at the IAB Plenary at IETF72, the author's Cheshire's discussion at the IAB Plenary at IETF72, the author's
understanding of Safari's operation with SRV records, Interactive understanding of Safari's operation with SRV records, Interactive
Connectivity Establishment (ICE [RFC5245]), and the current IPv4/IPv6 Connectivity Establishment (ICE [RFC5245]), the current IPv4/IPv6
behavior of SMTP mail transfer agents. behavior of SMTP mail transfer agents, and the implementation of
Happy Eyeballs in Google Chrome and Mozilla Firefox.
Thanks to Fred Baker, Jeff Kinzli, Christian Kuhtz, and Iljitsch van Thanks to Fred Baker, Jeff Kinzli, Christian Kuhtz, and Iljitsch van
Beijnum for fostering the creation of this document. Beijnum for fostering the creation of this document.
Thanks to Scott Brim, Rick Jones, Stig Venaas, Erik Kline, Bjoern Thanks to Scott Brim, Rick Jones, Stig Venaas, Erik Kline, Bjoern
Zeeb, Matt Miller, Dave Thaler, and Dmitry Anipko for providing Zeeb, Matt Miller, Dave Thaler, and Dmitry Anipko for providing
feedback on the document. feedback on the document.
Thanks to Javier Ubillos, Simon Perreault and Mark Andrews for the Thanks to Javier Ubillos, Simon Perreault and Mark Andrews for the
active feedback and the experimental work on the independent active feedback and the experimental work on the independent
practical implementations that they created. practical implementations that they created.
Also the authors would like to thank the following individuals who Also the authors would like to thank the following individuals who
participated in various email discussions on this topic: Mohacsi participated in various email discussions on this topic: Mohacsi
Janos, Pekka Savola, Ted Lemon, Carlos Martinez-Cagnazzo, Simon Janos, Pekka Savola, Ted Lemon, Carlos Martinez-Cagnazzo, Simon
Perreault, Jack Bates, Jeroen Massar, Fred Baker, Javier Ubillos, Perreault, Jack Bates, Jeroen Massar, Fred Baker, Javier Ubillos,
Teemu Savolainen, Scott Brim, Erik Kline, Cameron Byrne, Daniel Teemu Savolainen, Scott Brim, Erik Kline, Cameron Byrne, Daniel
Roesen, Guillaume Leclanche, Mark Smith, Gert Doering, Martin Roesen, Guillaume Leclanche, Mark Smith, Gert Doering, Martin
Millnert, Tim Durack, Matthew Palmer. Millnert, Tim Durack, Matthew Palmer.
11. IANA Considerations 9. IANA Considerations
This document has no IANA actions. This document has no IANA actions.
12. References 10. References
10.1. Normative References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. 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 [RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003. Protocol version 6 (IPv6)", RFC 3484, February 2003.
12.2. Informational References 10.2. Informational References
[Andrews] Andrews, M., "How to connect to a multi-homed server over [Andrews] Andrews, M., "How to connect to a multi-homed server over
TCP", January 2011, <http://www.isc.org/community/blog/ TCP", January 2011, <http://www.isc.org/community/blog/
201101/how-to-connect-to-a-multi-h omed-server-over-tcp>. 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] [Experiences]
Savolainen, T., Miettinen, N., Veikkolainen, S., Chown, Savolainen, T., Miettinen, N., Veikkolainen, S., Chown,
T., and J. Morse, "Experiences of host behavior in broken T., and J. Morse, "Experiences of host behavior in broken
IPv6 networks", March 2011, IPv6 networks", March 2011,
<http://www.ietf.org/proceedings/80/slides/v6ops-12.pdf>. <http://www.ietf.org/proceedings/80/slides/v6ops-12.pdf>.
[I-D.abarth-origin] [I-D.abarth-origin]
Barth, A., "The Web Origin Concept", Barth, A., "The Web Origin Concept",
draft-abarth-origin-09 (work in progress), November 2010. 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] [I-D.ietf-6man-addr-select-opt]
Matsumoto, A., Fujisaki, T., and J. Kato, "Distributing Matsumoto, A., Fujisaki, T., Kato, J., and T. Chown,
Address Selection Policy using DHCPv6", "Distributing Address Selection Policy using DHCPv6",
draft-ietf-6man-addr-select-opt-00 (work in progress), draft-ietf-6man-addr-select-opt-01 (work in progress),
December 2010. June 2011.
[Perreault] [Perreault]
Perreault, S., "Happy Eyeballs in Erlang", February 2011, Perreault, S., "Happy Eyeballs in Erlang", February 2011,
<http://www.viagenie.ca/news/ <http://www.viagenie.ca/news/
index.html#happy_eyeballs_erlang>. index.html#happy_eyeballs_erlang>.
[RFC1671] Carpenter, B., "IPng White Paper on Transition and Other [RFC1671] Carpenter, B., "IPng White Paper on Transition and Other
Considerations", RFC 1671, August 1994. 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 [RFC4436] Aboba, B., Carlson, J., and S. Cheshire, "Detecting
Network Attachment in IPv4 (DNAv4)", RFC 4436, March 2006. Network Attachment in IPv4 (DNAv4)", RFC 4436, March 2006.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT) (ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245, Traversal for Offer/Answer Protocols", RFC 5245,
April 2010. April 2010.
[RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for [RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for
Detecting Network Attachment in IPv6", RFC 6059, Detecting Network Attachment in IPv6", RFC 6059,
skipping to change at page 18, line 4 skipping to change at page 12, line 23
ilitychanged.aspx>. ilitychanged.aspx>.
[sop] W3C, "Same Origin Policy", January 2010, [sop] W3C, "Same Origin Policy", January 2010,
<http://www.w3.org/Security/wiki/Same_Origin_Policy>. <http://www.w3.org/Security/wiki/Same_Origin_Policy>.
[whitelist] [whitelist]
Google, "Google IPv6 DNS Whitelist", January 2009, Google, "Google IPv6 DNS Whitelist", January 2009,
<http://www.google.com/intl/en/ipv6>. <http://www.google.com/intl/en/ipv6>.
Appendix A. Changes Appendix A. Changes
A.1. changes from -01 to -02
A.1. changes from -02 to -03
o Re-casted this specification as a list of requirements for a
compliant algorithm, rather than trying to dictate a One True
algorithm.
A.2. changes from -01 to -02
o Now honors host's address preference (RFC3484 and friends) o Now honors host's address preference (RFC3484 and friends)
o No longer requires thread-safe DNS library. It uses getaddrinfo() o No longer requires thread-safe DNS library. It uses getaddrinfo()
o No longer describes threading. o No longer describes threading.
o IPv6 is given a 200ms head start (Initial Headstart variable). o IPv6 is given a 200ms head start (Initial Headstart variable).
o If the IPv6 and IPv4 connection attempts were made at nearly the o If the IPv6 and IPv4 connection attempts were made at nearly the
skipping to change at page 18, line 39 skipping to change at page 13, line 18
o If we didn't get both A and AAAA, abandon all Happy Eyeballs o If we didn't get both A and AAAA, abandon all Happy Eyeballs
processing (thanks to Simon Perreault). processing (thanks to Simon Perreault).
o added discussion of Same Origin Policy o added discussion of Same Origin Policy
o Removed discussion of NAT-PT and address learning; those are only o Removed discussion of NAT-PT and address learning; those are only
used with IPv6-only hosts whereas this document is about dual- used with IPv6-only hosts whereas this document is about dual-
stack hosts contacting dual-stack servers. stack hosts contacting dual-stack servers.
A.2. changes from -00 to -01 A.3. changes from -00 to -01
o added SRV section (thanks to Matt Miller) o added SRV section (thanks to Matt Miller)
Authors' Addresses Authors' Addresses
Dan Wing Dan Wing
Cisco Systems, Inc. Cisco Systems, Inc.
170 West Tasman Drive 170 West Tasman Drive
San Jose, CA 95134 San Jose, CA 95134
USA USA
Email: dwing@cisco.com Email: dwing@cisco.com
Andrew Yourtchenko Andrew Yourtchenko
Cisco Systems, Inc. Cisco Systems, Inc.
De Kleetlaan, 7 De Kleetlaan, 7
San Jose, Diegem B-1831 Diegem B-1831
Belgium Belgium
Email: ayourtch@cisco.com Email: ayourtch@cisco.com
 End of changes. 63 change blocks. 
454 lines changed or deleted 204 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/