draft-ietf-v6ops-happy-eyeballs-07.txt   rfc6555.txt 
v6ops D. Wing Internet Engineering Task Force (IETF) D. Wing
Internet-Draft A. Yourtchenko Request for Comments: 6555 A. Yourtchenko
Intended status: Standards Track Cisco Category: Standards Track Cisco
Expires: June 22, 2012 December 20, 2011 ISSN: 2070-1721 April 2012
Happy Eyeballs: Success with Dual-Stack Hosts Happy Eyeballs: Success with Dual-Stack Hosts
draft-ietf-v6ops-happy-eyeballs-07
Abstract Abstract
When a server's IPv4 path and protocol is working but the server's When a server's IPv4 path and protocol are working, but the server's
IPv6 path and protocol are not working, a dual-stack client IPv6 path and protocol are not working, a dual-stack client
application experiences significant connection delay compared to an application experiences significant connection delay compared to an
IPv4-only client. This is undesirable because it causes the dual- IPv4-only client. This is undesirable because it causes the dual-
stack client to have a worse user experience. This document stack client to have a worse user experience. This document
specifies requirements for algorithms that reduce this user-visible specifies requirements for algorithms that reduce this user-visible
delay, and provides an algorithm. delay and provides an algorithm.
Status of this Memo
This Internet-Draft is submitted in full conformance with the Status of This Memo
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This is an Internet Standards Track document.
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on June 22, 2012. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6555.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Additional Network and Host Traffic . . . . . . . . . . . 3 1.1. Additional Network and Host Traffic . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Hostnames . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Hostnames . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Delay When IPv6 is not Accessible . . . . . . . . . . . . 4 3.2. Delay When IPv6 Is Not Accessible . . . . . . . . . . . . 5
4. Algorithm Requirements . . . . . . . . . . . . . . . . . . . . 5 4. Algorithm Requirements . . . . . . . . . . . . . . . . . . . . 6
4.1. Delay IPv4 . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Delay IPv4 . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Stateful Behavior when IPv6 Fails . . . . . . . . . . . . 8 4.2. Stateful Behavior When IPv6 Fails . . . . . . . . . . . . 8
4.3. Reset on Network (re-)Initialization . . . . . . . . . . . 9 4.3. Reset on Network (Re-)Initialization . . . . . . . . . . . 9
4.4. Abandon Non-Winning Connections . . . . . . . . . . . . . 9 4.4. Abandon Non-Winning Connections . . . . . . . . . . . . . 9
5. Additional Considerations . . . . . . . . . . . . . . . . . . 10 5. Additional Considerations . . . . . . . . . . . . . . . . . . 10
5.1. Determining Address Type . . . . . . . . . . . . . . . . . 10 5.1. Determining Address Type . . . . . . . . . . . . . . . . . 10
5.2. Debugging and Troubleshooting . . . . . . . . . . . . . . 10 5.2. Debugging and Troubleshooting . . . . . . . . . . . . . . 10
5.3. Three or More Interfaces . . . . . . . . . . . . . . . . . 10 5.3. Three or More Interfaces . . . . . . . . . . . . . . . . . 10
5.4. A and AAAA Resource Records . . . . . . . . . . . . . . . 10 5.4. A and AAAA Resource Records . . . . . . . . . . . . . . . 10
5.5. Connection time out . . . . . . . . . . . . . . . . . . . 11 5.5. Connection Timeout . . . . . . . . . . . . . . . . . . . . 11
5.6. Interaction with Same Origin Policy . . . . . . . . . . . 11 5.6. Interaction with Same-Origin Policy . . . . . . . . . . . 11
5.7. Implementation Strategies . . . . . . . . . . . . . . . . 11 5.7. Implementation Strategies . . . . . . . . . . . . . . . . 12
6. Example Algorithm . . . . . . . . . . . . . . . . . . . . . . 12 6. Example Algorithm . . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 9.1. Normative References . . . . . . . . . . . . . . . . . . . 13
10.1. Normative References . . . . . . . . . . . . . . . . . . . 13 9.2. Informative References . . . . . . . . . . . . . . . . . . 13
10.2. Informational References . . . . . . . . . . . . . . . . . 13
Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . . 15
A.1. changes from -06 to -07 . . . . . . . . . . . . . . . . . 15
A.2. changes from -05 to -06 . . . . . . . . . . . . . . . . . 15
A.3. changes from -04 to -05 . . . . . . . . . . . . . . . . . 15
A.4. changes from -03 to -04 . . . . . . . . . . . . . . . . . 16
A.5. changes from -03 to -04 . . . . . . . . . . . . . . . . . 16
A.6. changes from -02 to -03 . . . . . . . . . . . . . . . . . 16
A.7. changes from -01 to -02 . . . . . . . . . . . . . . . . . 16
A.8. changes from -00 to -01 . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
In order to use applications over IPv6, it is necessary that users In order to use applications over IPv6, it is necessary that users
enjoy nearly identical performance as compared to IPv4. A enjoy nearly identical performance as compared to IPv4. A
combination of today's applications, IPv6 tunneling, 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 does not scale well (to the number of DNS servers However, this does not scale well (to the number of DNS servers
worldwide or the number of content providers worldwide), and does not worldwide or the number of content providers worldwide) and does
react to intermittent network path outages. react to intermittent network path outages.
Instead, applications reduce connection setup delays themselves, by Instead, applications reduce connection setup delays themselves, by
more aggressively making connections on IPv6 and IPv4. There are a more aggressively making connections on IPv6 and IPv4. There are a
variety of algorithms that can be envisioned. This document variety of algorithms that can be envisioned. This document
specifies requirements for any such algorithm, with the goals that specifies requirements for any such algorithm, with the goals that
the network and servers are not inordinately harmed with a simple the network and servers not be inordinately harmed with a simple
doubling of traffic on IPv6 and IPv4, and the host's address doubling of traffic on IPv6 and IPv4 and the host's address
preference is honored (e.g., [RFC3484]). preference be honored (e.g., [RFC3484]).
1.1. Additional Network and Host Traffic 1.1. 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, especially when connections to the recommendations in this document, especially when connections
to the preferred address family (usually IPv6) are not completing to the preferred address family (usually IPv6) are not completing
quickly. 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 and, most importantly, to reduce the load on
network address translators). The improvement in the user experience IPv4 network address translators). The user experience is improved
benefits the user to only a small detriment of the network, DNS to the slight detriment of the network, DNS server, and server that
server, and server that are serving the user. are serving the user.
2. Notational Conventions 2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Problem Statement 3. Problem Statement
The basis of the IPv6/IPv4 selection problem was first described in The basis of the IPv6/IPv4 selection problem was first described in
1994 in [RFC1671], 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
stack approach is no better than the packet translation dual-stack approach is no better than the packet translation
approach.)" approach.)
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 hostname be used for IPv4 and IPv6. same hostname be used for IPv4 and IPv6.
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 is slower than
IPv4 connectivity. native IPv4 connectivity.
The mechanism described in this document is directly applicable to The mechanism described in this document is directly applicable to
connection-oriented transports (e.g., TCP, SCTP), which is the scope connection-oriented transports (e.g., TCP, SCTP), which is the scope
of this document. For connectionless transport protocols (e.g., of this document. For connectionless transport protocols (e.g.,
UDP), a similar mechanism can be used if the application has request/ UDP), a similar mechanism can be used if the application has request/
response semantics (e.g., as done by ICE to select a working IPv6 or response semantics (e.g., as done by Interactive Connectivity
IPv4 media path [RFC6157]). Establishment (ICE) to select a working IPv6 or IPv4 media path
[RFC6157]).
3.1. Hostnames 3.1. Hostnames
Hostnames are often used between users to exchange pointers to Hostnames are often used between users to exchange pointers to
content -- such as on social networks, email, instant messaging, or content -- such as on social networks, email, instant messaging, or
other systems. Using separate namespaces (e.g., "ipv6.example.com") other systems. Using separate namespaces (e.g., "ipv6.example.com"),
which are only accessible with certain client technology (e.g., an which are only accessible with certain client technology (e.g., an
IPv6 client) and dependencies (e.g., a working IPv6 path) causes IPv6 client) and dependencies (e.g., a working IPv6 path), causes
namespace fragmentation and reduces the ability for users to share namespace fragmentation and reduces the ability for users to share
hostnames. It also complicates printed material that includes the hostnames. It also complicates printed material that includes the
hostname. hostname.
The algorithm described in this document allows production hostnames The algorithm described in this document allows production hostnames
to avoid these problematic references to IPv4 or IPv6. to avoid these problematic references to IPv4 or IPv6.
3.2. Delay When IPv6 is not Accessible 3.2. Delay When IPv6 Is Not Accessible
When IPv6 connectivity is impaired, today's IPv6-capable applications When IPv6 connectivity is impaired, today's IPv6-capable applications
(e.g., web browsers, email clients, instant messaging clients) incur (e.g., web browsers, email clients, instant messaging clients) incur
many seconds of delay before falling back to IPv4. This delays many seconds of delay before falling back to IPv4. This delays
overall application operation, including harming the user's overall application operation, including harming the user's
experience with IPv6, which will slow the acceptance of IPv6, because experience with IPv6, which will slow the acceptance of IPv6, because
IPv6 is frequently disabled in its entirety on the end systems to IPv6 is frequently disabled in its entirety on the end systems to
improve the user experience. improve the user experience.
Reasons for such failure include no connection to the IPv6 Internet, Reasons for such failure include no connection to the IPv6 Internet,
skipping to change at page 5, line 32 skipping to change at page 5, line 38
4. |---2001:db8::1----------->| | 4. |---2001:db8::1----------->| |
5. | | | 5. | | |
6. | |==TCP SYN, IPv6===>X | 6. | |==TCP SYN, IPv6===>X |
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. Algorithm Requirements 4. Algorithm Requirements
A Happy Eyeballs algorithm has two primary goals: A "Happy Eyeballs" algorithm has two primary goals:
1. Provides fast connection for users, by quickly attempting to 1. Provides fast connection for users, by quickly attempting to
connect using IPv6 and (if that connection attempt is not quickly connect using IPv6 and (if that connection attempt is not quickly
successful) to connect using IPv4. successful) to connect using IPv4.
2. Avoids thrashing the network, by not (always) making simultaneous 2. Avoids thrashing the network, by not (always) making simultaneous
connection attempts on both IPv6 and IPv4. connection attempts on both IPv6 and IPv4.
The basic idea is depicted in the following diagram: The basic idea is depicted in the following diagram:
skipping to change at page 6, line 23 skipping to change at page 6, line 31
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------->|
8. | |<-TCP SYN+ACK, IPv4----| 8. | |<-TCP SYN+ACK, IPv4----|
9. | |--TCP ACK, IPv4------->| 9. | |--TCP ACK, IPv4------->|
10. | |==TCP SYN, IPv6===>X | 10. | |==TCP SYN, IPv6===>X |
Figure 2: Happy Eyeballs flow 1, IPv6 broken Figure 2: Happy Eyeballs Flow 1, IPv6 Broken
In the diagram above, the client sends two TCP SYNs at the same time 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 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 but has little impact to the user because there is no long delay
before using IPv4. The IPv6 path is retried until the application before using IPv4. The IPv6 path is retried until the application
gives up (10). gives up (10).
After performing the above procedure, the client learns whether After performing the above procedure, the client learns whether
connections to the host's IPv6 or IPv4 address were successful. The connections to the host's IPv6 or IPv4 address were successful. The
client MUST cache information regarding the outcome of each client MUST cache information regarding the outcome of each
connection attempt and uses that information to avoid thrashing the connection attempt, and it uses that information to avoid thrashing
network with subsequent attempts. For example, in the example above, the network with subsequent attempts. In the example above, the
the cache indicates that the IPv6 connection attempt failed, and cache indicates that the IPv6 connection attempt failed, and
therefore the system will prefer IPv4 instead. Cache entries should therefore the system will prefer IPv4 instead. Cache entries should
be flushed when their age exceeds a system defined maximum on the be flushed when their age exceeds a system-defined maximum on the
order of ten minutes. order of 10 minutes.
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=======>| 6. | |==TCP SYN, IPv6=======>|
7. | |--TCP SYN, IPv4------->| 7. | |--TCP SYN, IPv4------->|
8. | |<=TCP SYN+ACK, IPv6====| 8. | |<=TCP SYN+ACK, IPv6====|
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).
Any Happy Eyeballs algorithm will persist in products for as long as 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 the client host is dual-stacked, which will persist as long as there
are IPv4-only servers on the Internet -- the so-called "long tail". are IPv4-only servers on the Internet -- the so-called "long tail".
Over time, as most content is available via IPv6, the amount of IPv4 Over time, as most content is available via IPv6, the amount of IPv4
traffic will decrease. This means that the IPv4 infrastructure will, traffic will decrease. This means that the IPv4 infrastructure will,
over time, be sized to accommodate that decreased (and decreasing) over time, be sized to accommodate that decreased (and decreasing)
amount of traffic. It is critical that a Happy Eyeballs algorithm amount of traffic. It is critical that a Happy Eyeballs algorithm
not cause a surge of unnecessary traffic on that IPv4 infrastructure. not cause a surge of unnecessary traffic on that IPv4 infrastructure.
To meet that goal, compliant Happy Eyeballs algorithms must adhere to To meet that goal, compliant Happy Eyeballs algorithms must adhere to
the requirements in this section. the requirements in this section.
4.1. Delay IPv4 4.1. Delay IPv4
The transition to IPv6 is likely to produce a mix of different hosts The transition to IPv6 is likely to produce a mix of different hosts
within a subnetwork -- hosts that are IPv4-only, hosts that are IPv6- within a subnetwork -- hosts that are IPv4-only, hosts that are IPv6-
only (e.g., sensors), and dual-stack. This mix of hosts will exist only (e.g., sensors), and dual-stack hosts. This mix of hosts will
both within an administrative domain (a single home, enterprise, exist both within an administrative domain (a single home,
hotel, or coffee shop) and between administrative domains. For enterprise, hotel, or coffee shop) and between administrative
example, a single home might have an IPv4-only television in one room domains. For example, a single home might have an IPv4-only
and a dual-stack television in another room. As another example, television in one room and a dual-stack television in another room.
another subscriber might have hosts that are all capable of dual- As another example, another subscriber might have hosts that are all
stack operation. capable of dual-stack operation.
Due to IPv4 exhaustion, it is likely that a subscriber's hosts (both Due to IPv4 exhaustion, it is likely that a subscriber's hosts (both
IPv4-only hosts and dual-stack hosts) will be sharing an IPv4 address IPv4-only hosts and dual-stack hosts) will be sharing an IPv4 address
with other subscribers. The dual-stack hosts have an advantage: with other subscribers. The dual-stack hosts have an advantage: they
they can utilize IPv6 or IPv4, which means it can utilize the can utilize IPv6 or IPv4, which means they can utilize the technique
technique described in this document. The IPv4-only hosts have a described in this document. The IPv4-only hosts have a disadvantage:
disadvantage: they can only utilize IPv4. If all hosts (dual-stack
and IPv4-only) are using IPv4, there is additional contention for the they can only utilize IPv4. If all hosts (dual-stack and IPv4-only)
shared IPv4 address. The IPv4-only hosts cannot avoid that are using IPv4, there is additional contention for the shared IPv4
contention (as they can only use IPv4) while the dual-stack hosts can address. The IPv4-only hosts cannot avoid that contention (as they
avoid that contention by using IPv6. can only use IPv4), while the dual-stack hosts can avoid it by using
IPv6.
As dual-stack hosts proliferate and content becomes available over As dual-stack hosts proliferate and content becomes available over
IPv6, there will be proportionally less IPv4 traffic. This is true IPv6, there will be proportionally less IPv4 traffic. This is true
especially for dual-stack hosts that do not implement Happy Eyeballs, especially for dual-stack hosts that do not implement Happy Eyeballs,
because those dual-stack hosts have a very strong preference to use because those dual-stack hosts have a very strong preference to use
IPv6 (with timeouts in the tens of seconds before they will attempt IPv6 (with timeouts in the tens of seconds before they will attempt
to use IPv4). to use IPv4).
When deploying IPv6, both content providers and Internet Service When deploying IPv6, both content providers and Internet Service
Providers (who supply IPv4 address sharing mechanisms such as Carrier Providers (who supply mechanisms for IPv4 address sharing such as
Grade NAT (CGN)) will want to reduce their investment in IPv4 Carrier-Grade NAT (CGN)) will want to reduce their investment in IPv4
equipment -- load balancers, peering links, and address sharing equipment -- load-balancers, peering links, and address sharing
devices. If a Happy Eyeballs implementation treats IPv6 and IPv4 devices. If a Happy Eyeballs implementation treats IPv6 and IPv4
equally by connecting to whichever address family is fastest, it will equally by connecting to whichever address family is fastest, it will
contribute to load on IPv4. This load impacts IPv4-only devices (by contribute to load on IPv4. This load impacts IPv4-only devices (by
increasing contention of IPv4 address sharing and increasing load on increasing contention of IPv4 address sharing and increasing load on
IPv4 load balancers). Because of this, ISPs and content providers IPv4 load-balancers). Because of this, ISPs and content providers
will find it impossible to reduce their investment in IPv4 equipment. will find it impossible to reduce their investment in IPv4 equipment.
This means that costs to migrate to IPv6 are increased, because the This means that costs to migrate to IPv6 are increased because the
investment in IPv4 cannot be reduced. Furthermore, using only a investment in IPv4 cannot be reduced. Furthermore, using only a
metric that measures connection speed ignores the value of IPv6 over metric that measures the connection speed ignores the benefits that
IPv4 address sharing, such as shared penalty boxes and geo-location IPv6 brings when compared with IPv4 address sharing, such as improved
[RFC6269]. geo-location [RFC6269] and the lack of fate-sharing due to traversing
a large translator.
Thus, to avoid harming IPv4-only hosts which can only utilize IPv4, Thus, to avoid harming IPv4-only hosts, implementations MUST prefer
implementations MUST prefer the first IP address family returned by the first IP address family returned by the host's address preference
the host's address preference policy, unless implementing a stateful policy, unless implementing a stateful algorithm described in
algorithm described in Section 4.2. This usually means giving Section 4.2. This usually means giving preference to IPv6 over IPv4,
preference to IPv6 over IPv4, although that preference can be over- although that preference can be overridden by user configuration or
ridden by user configuration or by network configuration by network configuration [ADDR-SELECT]. If the host's policy is
[I-D.ietf-6man-addr-select-opt]. If the host's policy is unknown or unknown or not attainable, implementations MUST prefer IPv6 over
not attainable, implementations MUST prefer IPv6 over IPv4. IPv4.
4.2. Stateful Behavior when IPv6 Fails 4.2. Stateful Behavior When IPv6 Fails
Some Happy Eyeballs algorithms are stateful -- that is, the algorithm Some Happy Eyeballs algorithms are stateful -- that is, the algorithm
will remember that IPv6 always fails, or that IPv6 to certain will remember that IPv6 always fails, or that IPv6 to certain
prefixes always fails, and so on. This section describes such prefixes always fails, and so on. This section describes such
algorithms. Stateless algorithms, which do not remember the success/ algorithms. Stateless algorithms, which do not remember the success/
failure of previous connections, are not discussed in this section. failure of previous connections, are not discussed in this section.
After making a connection attempt on the preferred address family After making a connection attempt on the preferred address family
(e.g., IPv6), and failing to establish a connection within a certain (e.g., IPv6) and failing to establish a connection within a certain
time period (see Section 5.5), a Happy Eyeballs implementation will time period (see Section 5.5), a Happy Eyeballs implementation will
decide to initiate a second connection attempt using the same address decide to initiate a second connection attempt using the same address
family or the other address family. family or the other address family.
Such an implementation MAY make subsequent connection attempts (to Such an implementation MAY make subsequent connection attempts (to
the same host or to other hosts) on the successful address family the same host or to other hosts) on the successful address family
(e.g., IPv4). So long as new connections are being attempted by the (e.g., IPv4). So long as new connections are being attempted by the
host, such an implementation MUST occasionally make connection host, such an implementation MUST occasionally make connection
attempts using the host's preferred address family, as it may have attempts using the host's preferred address family, as it may have
become functional again, and it SHOULD do so every 10 minutes. The become functional again, and it SHOULD do so every 10 minutes. The
10 minute delay before re-trying a failed address family avoids the 10-minute delay before retrying a failed address family avoids the
simple doubling of connection attempts on both IPv6 and IPv4. simple doubling of connection attempts on both IPv6 and IPv4.
Implementation note: this can be achieved by flushing Happy Eyeballs Implementation note: this can be achieved by flushing Happy Eyeballs
state every every 10 minutes, which does not significantly harm the state every 10 minutes, which does not significantly harm the
application's subsequent connection setup time. If connections using application's subsequent connection setup time. If connections using
the preferred address family are again successful, the preferred the preferred address family are again successful, the preferred
address family SHOULD be used for subsequent connections. Because address family SHOULD be used for subsequent connections. Because
this implementation is stateful, it MAY track connection success (or this implementation is stateful, it MAY track connection success (or
failure) based on IPv6 or IPv4 prefix (e.g., connections to the same failure) based on IPv6 or IPv4 prefix (e.g., connections to the same
prefix assigned to the interface are successful whereas connections prefix assigned to the interface are successful whereas connections
to other prefixes are failing). to other prefixes are failing).
4.3. Reset on Network (re-)Initialization 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), a Happy Eyeballs algorithm SHOULD broken IPv6 or IPv4 connectivity), a Happy Eyeballs algorithm SHOULD
re-initialize when the interface is connected to a new network. re-initialize when the interface is connected to a new network.
Interfaces can determine network (re-)initialization by a variety of Interfaces can determine network (re-)initialization by a variety of
mechanisms (e.g., DNAv4 [RFC4436], DNAv6 [RFC6059]). mechanisms (e.g., Detecting Network Attachment in IPv4 (DNAv4)
[RFC4436], DNAv6 [RFC6059]).
If the client application is a web browser, see also Section 5.6. If the client application is a web browser, see also Section 5.6.
4.4. Abandon Non-Winning Connections 4.4. Abandon Non-Winning Connections
It is RECOMMENDED that the non-winning connections be abandoned, even It is RECOMMENDED that the non-winning connections be abandoned, even
though they could -- in some cases -- be put to reasonable use. though they could -- in some cases -- be put to reasonable use.
Justification: This reduces the load on the server (file Justification: This reduces the load on the server (file
descriptors, TCP control blocks), stateful middleboxes (NAT and descriptors, TCP control blocks) and stateful middleboxes (NAT and
firewalls) and, if the abandoned connection is IPv4, reduces IPv4 firewalls). Also, if the abandoned connection is IPv4, this
address sharing contention. reduces IPv4 address sharing contention.
HTTP: The design of some sites can break because of HTTP cookies HTTP: The design of some sites can break because of HTTP cookies
that incorporate the client's IP address and require all that incorporate the client's IP address and require all
connections be from the same IP address. If some connections from connections be from the same IP address. If some connections from
the same client are arriving from different IP addresses (or the same client are arriving from different IP addresses (or
worse, different IP address families), such applications will worse, different IP address families), such applications will
break. Additionally for HTTP, using the non-winning connection break. Additionally, for HTTP, using the non-winning connection
can interfere with the browser's Same Origin Policy (see can interfere with the browser's same-origin policy (see
Section 5.6). Section 5.6).
5. Additional Considerations 5. Additional Considerations
This section discusses considerations related to Happy Eyeballs. This section discusses considerations related to Happy Eyeballs.
5.1. Determining Address Type 5.1. 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, IPv6/ an A query). While IPv6/IPv4 translation makes that difficult, IPv6/
IPv4 translators do not need to be deployed on networks with dual IPv4 translators do not need to be deployed on networks with dual-
stack clients, because dual stack clients can use their native IP stack clients because dual-stack clients can use their native IP
address family. address family.
5.2. Debugging and Troubleshooting 5.2. 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 a techniques are by default less useful for diagnosing issues with a
particular address family. To assist in that regard, the particular address family. To assist in that regard, the
implementations MAY also provide a mechanism to disable their Happy implementations MAY also provide a mechanism to disable their Happy
Eyeballs behavior via a user setting, and to provide data useful for Eyeballs behavior via a user setting, and to provide data useful for
debugging (e.g., a log or way to review current preferences). debugging (e.g., a log or way to review current preferences).
5.3. Three or More Interfaces 5.3. Three or More Interfaces
A dual-stack host normally has two logical interfaces: an IPv6 A dual-stack host normally has two logical interfaces: an IPv6
interface and an IPv4 interface. However, a dual-stack host might interface and an IPv4 interface. However, a dual-stack host might
have more than two logical interfaces because of a VPN (where a third have more than two logical interfaces because of a VPN (where a third
interface is the tunnel address, often assigned by the remote interface is the tunnel address, often assigned by the remote
corporate network) or because of multiple physical interfaces such as corporate network), because of multiple physical interfaces such as
wired and wireless Ethernet, because the host belongs to multiple wired and wireless Ethernet, because the host belongs to multiple
VLANs, or other reasons. The interaction of Happy Eyeballs with more VLANs, or other reasons. The interaction of Happy Eyeballs with more
than two logical interfaces is for further study. than two logical interfaces is for further study.
5.4. A and AAAA Resource Records 5.4. A and AAAA Resource Records
It is possible that an DNS query for an A or AAAA resource record It is possible that a DNS query for an A or AAAA resource record will
will return more than one A or AAAA address. When this occurs, it is return more than one A or AAAA address. When this occurs, it is
RECOMMENDED that a Happy Eyeballs implementation order the responses RECOMMENDED that a Happy Eyeballs implementation order the responses
following the host's address preference policy and then try the first following the host's address preference policy and then try the first
address. If that fails after a certain time (see Section 5.5), the address. If that fails after a certain time (see Section 5.5), the
next address SHOULD be the IPv4 address. next address SHOULD be the IPv4 address.
If that fails to connect after a certain time (see Section 5.5), a If that fails to connect after a certain time (see Section 5.5), a
Happy Eyeballs implementation SHOULD try the other addresses Happy Eyeballs implementation SHOULD try the other addresses
returned; the order of these connection attempts is not important. returned; the order of these connection attempts is not important.
On the Internet today, servers commonly have multiple A records to On the Internet today, servers commonly have multiple A records to
provide load balancing across their servers. This same technique provide load-balancing across their servers. This same technique
would be useful for AAAA records, as well. However, if multiple AAAA would be useful for AAAA records, as well. However, if multiple AAAA
records are returned to a non-Happy Eyeballs client that has broken records are returned to a client that is not using Happy Eyeballs and
IPv6 connectivity, it will further increase the delay to fall back to that has broken IPv6 connectivity, it will further increase the delay
IPv4. Thus, web site operators with native IPv6 connectivity SHOULD to fall back to IPv4. Thus, web site operators with native IPv6
NOT offer multiple AAAA records. If Happy Eyeballs is widely connectivity SHOULD NOT offer multiple AAAA records. If Happy
deployed in the future, this recommendation might be revisited. Eyeballs is widely deployed in the future, this recommendation might
be revisited.
5.5. Connection time out 5.5. Connection Timeout
The primary purpose of Happy Eyeballs is to reduce the wait time for The primary purpose of Happy Eyeballs is to reduce the wait time for
a dual stack connection to complete, especially when the IPv6 path is a dual-stack connection to complete, especially when the IPv6 path is
broken and IPv6 is preferred. Aggressive time outs (on the order of broken and IPv6 is preferred. Aggressive timeouts (on the order of
tens of milliseconds) achieve this goal, but at the cost of network tens of milliseconds) achieve this goal, but at the cost of network
traffic. This network traffic may be billable on certain networks, traffic. This network traffic may be billable on certain networks,
will create state on some middleboxes (e.g., firewalls, IDS, NAT), will create state on some middleboxes (e.g., firewalls, intrusion
and will consume ports if IPv4 addresses are shared. For these detection systems, NATs), and will consume ports if IPv4 addresses
reasons, it is RECOMMENDED that connection attempts be paced to give are shared. For these reasons, it is RECOMMENDED that connection
connections a chance to complete. It is RECOMMENDED that connections attempts be paced to give connections a chance to complete. It is
attempts be paced 150-250ms apart, to balance human factors against RECOMMENDED that connection attempts be paced 150-250 ms apart to
network load. Stateful algorithms are expected to be more aggressive balance human factors against network load. Stateful algorithms are
(that is, make connection attempts closer together), as stateful expected to be more aggressive (that is, make connection attempts
algorithms maintain an estimate of the expected connection completion closer together), as stateful algorithms maintain an estimate of the
time. expected connection completion time.
5.6. Interaction with Same Origin Policy 5.6. Interaction with Same-Origin Policy
Web browsers implement a Same Origin Policy [RFC6454] which causes Web browsers implement a same-origin policy [RFC6454] that causes
subsequent connections to the same hostname to go to the same IPv4 subsequent connections to the same hostname to go to the same IPv4
(or IPv6) address as the previous successful connection. This is (or IPv6) address as the previous successful connection. This is
done to prevent certain types of attacks. done to prevent certain types of 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, as that would their same-origin policy because of Happy Eyeballs, as that would
create an additional security exposure. create an additional security exposure.
5.7. Implementation Strategies 5.7. Implementation Strategies
The simplest venue for implementation of Happy Eyeballs is within the The simplest venue for the implementation of Happy Eyeballs is within
application itself. The algorithm specified in this document is the application itself. The algorithm specified in this document is
relatively simple to implement, and would require no specific support relatively simple to implement and would require no specific support
from the operating system beyond the commonly-available APIs that from the operating system beyond the commonly available APIs that
provide transport service. It could also be added to applications by provide transport service. It could also be added to applications by
way of a specific Happy Eyeballs API, replacing or augmenting the way of a specific Happy Eyeballs API, replacing or augmenting the
transport service APIs. transport service APIs.
To improve IPv6 connectivity experience for legacy applications To improve the IPv6 connectivity experience for legacy applications
(e.g., applications which simply rely on the operating system's (e.g., applications that simply rely on the operating system's
address preference order), operating systems may consider more address preference order), operating systems may consider more
sophisticated approaches. These can include changing default address sophisticated approaches. These can include changing default address
selection sorting ([RFC3484]) based on configuration received from selection sorting [RFC3484] based on configuration received from the
the network, or observing connection failures to IPv6 and IPV4 network, or observing connection failures to IPv6 and IPV4
destinations. destinations.
6. Example Algorithm 6. Example Algorithm
What follows is the algorithm implemented in Google Chrome and What follows is the algorithm implemented in Google Chrome and
Mozilla Firefox. Mozilla Firefox.
1. Call getaddinfo(), which returns a list of IP addresses sorted by 1. Call getaddinfo(), which returns a list of IP addresses sorted by
the host's address preference policy. the host's address preference policy.
2. Initiate a connection attempt with the first address in that list 2. Initiate a connection attempt with the first address in that list
(e.g., IPv6). (e.g., IPv6).
3. If that connection does not complete within a short period of 3. If that connection does not complete within a short period of
time (Firefox and Chrome use 300ms), initiate a connection time (Firefox and Chrome use 300 ms), initiate a connection
attempt with the first address belonging to the other address attempt with the first address belonging to the other address
family (e.g., IPv4) family (e.g., IPv4).
4. The first connection that is established is used. The other 4. The first connection that is established is used. The other
connection is discarded. connection is discarded.
If an algorithm were to cache connection success/failure, the caching If an algorithm were to cache connection success/failure, the caching
would occur after step 4 determined which connection was successful. would occur after step 4 determined which connection was successful.
Other example algorithms include [Perreault] and [Andrews]. Other example algorithms include [Perreault] and [Andrews].
7. Security Considerations 7. Security Considerations
See Section 4.4 and Section 5.6. See Sections 4.4 and 5.6.
8. Acknowledgements 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 IETF 72, the author's
understanding of Safari's operation with SRV records, Interactive understanding of Safari's operation with SRV records, ICE [RFC5245],
Connectivity Establishment (ICE [RFC5245]), the current IPv4/IPv6 the current IPv4/IPv6 behavior of SMTP mail transfer agents, and the
behavior of SMTP mail transfer agents, and the implementation of implementation of Happy Eyeballs in Google Chrome and Mozilla
Happy Eyeballs in Google Chrome and Mozilla Firefox. 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, Dmitry Anipko, Brian Carpenter, and Zeeb, Matt Miller, Dave Thaler, Dmitry Anipko, Brian Carpenter, and
David Crocker for their feedback. David Crocker for their feedback.
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, and Matthew Palmer.
9. IANA Considerations
This document has no IANA actions.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
10.2. 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>.
[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.ietf-6man-addr-select-opt]
Matsumoto, A., Fujisaki, T., Kato, J., and T. Chown,
"Distributing Address Selection Policy using DHCPv6",
draft-ietf-6man-addr-select-opt-01 (work in progress),
June 2011.
[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.
[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.
[RFC6157] Camarillo, G., El Malki, K., and V. Gurbani, "IPv6
Transition in the Session Initiation Protocol (SIP)",
RFC 6157, April 2011.
[RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing", RFC 6269,
June 2011.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
December 2011.
[whitelist]
Google, "Google IPv6 DNS Whitelist", January 2009,
<http://www.google.com/intl/en/ipv6>.
Appendix A. Changes
[RFC Editor: Please remove this section prior to publication as an
RFC.]
A.1. changes from -06 to -07
o Changed "xmpp clients" to "instant messaging clients".
o For debugging/troubleshooting, providing a log of activity or a
way to see current settings is useful.
o tweaked abstract
o "URIs and hostnames" -> "hostnames"
o tweaked text on caching
o interfaces (not hosts) notice when they are connected to a new
network.
o encourage implementations to provide log or other way to view
Happy Eyeballs settings.
o detailed that implementation can be in OS or in application.
o 150-250ms is for human factors
A.2. changes from -05 to -06
o Added paragraph describing current AAAA practice on the Internet
(one AAAA record) due to non-Happy Eyeballs implementations, per
opsdir review.
o fixed "=" in Figure 1.
o Removed text discussing A6. A6 is being deprecated in another
document, and querying A6 is not a significant operational problem
on the Internet.
A.3. changes from -04 to -05
o Updated citations.
A.4. changes from -03 to -04
o Make RFC3363 a non-normative reference.
A.5. changes from -03 to -04
o Better explained why IPv6 needs to be preferred 9. References
o Don't query A6. 9.1. Normative References
A.6. changes from -02 to -03 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
o Re-casted this specification as a list of requirements for a [RFC3484] Draves, R., "Default Address Selection for Internet
compliant algorithm, rather than trying to dictate a One True Protocol version 6 (IPv6)", RFC 3484, February 2003.
algorithm.
A.7. changes from -01 to -02 9.2. Informative References
o Now honors host's address preference (RFC3484 and friends) [ADDR-SELECT] Matsumoto, A., Fujisaki, T., Kato, J., and T. Chown,
"Distributing Address Selection Policy using DHCPv6",
Work in Progress, February 2012.
o No longer requires thread-safe DNS library. It uses getaddrinfo() [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-homed-server-
over-tcp>.
o No longer describes threading. [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>.
o IPv6 is given a 200ms head start (Initial Headstart variable). [Perreault] Perreault, S., "Happy Eyeballs in Erlang", February
2011, <http://www.viagenie.ca/news/
index.html#happy_eyeballs_erlang>.
o If the IPv6 and IPv4 connection attempts were made at nearly the [RFC1671] Carpenter, B., "IPng White Paper on Transition and
same time, wait Tolerance Interval milliseconds for both to Other Considerations", RFC 1671, August 1994.
complete before deciding which one wins.
o Renamed "global P" to "Smoothed P", and better described how it is [RFC4436] Aboba, B., Carlson, J., and S. Cheshire, "Detecting
calculated. Network Attachment in IPv4 (DNAv4)", RFC 4436, March
2006.
o introduced the exception cache. This contains the set of networks [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
that only work with IPv4 (or only with IPv6), so that subsequent (ICE): A Protocol for Network Address Translator (NAT)
connection attempts use that address family without them causing Traversal for Offer/Answer Protocols", RFC 5245, April
serious affect to Smoothed P. 2010.
o encourages that every 10 minutes the exception cache and Smoothed [RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for
P be reset. This allows IPv6 to be attempted again, so we don't Detecting Network Attachment in IPv6", RFC 6059,
get 'stuck' on IPv4. November 2010.
o If we didn't get both A and AAAA, abandon all Happy Eyeballs [RFC6157] Camarillo, G., El Malki, K., and V. Gurbani, "IPv6
processing (thanks to Simon Perreault). Transition in the Session Initiation Protocol (SIP)",
RFC 6157, April 2011.
o added discussion of Same Origin Policy [RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
o Removed discussion of NAT-PT and address learning; those are only Roberts, "Issues with IP Address Sharing", RFC 6269,
used with IPv6-only hosts whereas this document is about dual- June 2011.
stack hosts contacting dual-stack servers.
A.8. changes from -00 to -01 [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, December
2011.
o added SRV section (thanks to Matt Miller) [WHITELIST] Google, "Google over IPv6",
<http://www.google.com/intl/en/ipv6>.
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
Diegem B-1831 Diegem B-1831
Belgium Belgium
Email: ayourtch@cisco.com EMail: ayourtch@cisco.com
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