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draft-ietf-ice-dualstack-fairness.xml
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<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?>
<?rfc tocompact="yes"?>
<?rfc tocdepth="3"?>
<?rfc tocindent="yes"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes"?>
<?rfc comments="yes"?>
<?rfc inline="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<rfc category="info" docName="draft-ietf-ice-dualstack-fairness-latest"
ipr="trust200902">
<front>
<title abbrev="ICE Multihomed and DualStack Fairness ">ICE Multihomed and IPv4/IPv6 Dual Stack Fairness</title>
<author fullname="Paal-Erik Martinsen" initials="P.E" surname="Martinsen">
<organization abbrev="Cisco">Cisco Systems, Inc.</organization>
<address>
<postal>
<street>Philip Pedersens Vei 22</street>
<city>Lysaker</city>
<region>Akershus</region>
<code>1325</code>
<country>Norway</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Tirumaleswar Reddy" initials="T." surname="Reddy">
<organization abbrev="Cisco">Cisco Systems, Inc.</organization>
<address>
<postal>
<street>Cessna Business Park, Varthur Hobli</street>
<street>Sarjapur Marathalli Outer Ring Road</street>
<city>Bangalore</city>
<region>Karnataka</region>
<code>560103</code>
<country>India</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Prashanth Patil" initials="P." surname="Patil">
<organization abbrev="Cisco">Cisco Systems, Inc.</organization>
<address>
<postal>
<street/>
<city>Bangalore</city>
<country>India</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<date/>
<workgroup>ICE</workgroup>
<abstract>
<t>
This document provides guidelines on how to make Interactive
Connectivity Establishment (ICE) conclude faster in multihomed
and IPv4/IPv6 dual-stack scenarios where broken paths
exist. The provided guidelines are backwards compatible with
the original ICE specification.
</t>
</abstract>
</front>
<middle>
<section anchor="introduction" title="Introduction">
<t>
Applications should take special care to deprioritize network
interfaces known to provide unreliable connectivity when
operating in a multihomed environment. For example certain
tunnel services might provide unreliable connectivity. Doing so
will ensure a more fair distribution of the connectivity
checks across available network interfaces on the device. The
simple guidelines presented here describes how to deprioritize
interfaces known by the application to provide unreliable
connectivity.
</t>
<t>
There is a also a need to introduce more fairness when
handling connectivity checks for different IP address families
in dual-stack IPv4/IPv6 ICE scenarios. Section 4.1.2.1 of ICE
<xref target="RFC5245"/> points to <xref target="RFC3484"/>
for prioritizing among the different IP families. <xref
target="RFC3484"/> is obsoleted by <xref target="RFC6724"/>
but following the recommendations from the updated RFC will
lead to prioritization of IPv6 over IPv4 for the same
candidate type. Due to this, connectivity checks for
candidates of the same type (host, reflexive or relay) are
sent such that an IP address family is completely depleted
before checks from the other address family are started. This
results in user noticeable setup delays if the path for the
prioritized address family is broken.
</t>
<t>
To avoid such user noticeable delays when either IPv6 or IPv4
path is broken or excessive slow, this specification
encourages intermingling the different address families when
connectivity checks are performed. Introducing IP address
family fairness into ICE connectivity checks will lead to more
sustained dual-stack IPv4/IPv6 deployment as users will no
longer have an incentive to disable IPv6. The cost is a small
penalty to the address type that otherwise would have been
prioritized.
</t>
<t>
This document describes how to fairly order the candidates in
multihomed and dual-stack environments, thus affecting the
sending order of the connectivity checks. If aggressive
nomination is in use, this will have an effect on what
candidate pair ends up as the active one. Ultimately it should
be up to the agent to decide what candidate pair is best
suited for transporting media.
</t>
<t>
The guidelines outlined in this specification are backward
compatible with a standard ICE implementation. This
specification only alters the values used to create the
resulting checklists in such a way that the core mechanisms
from ICE <xref target="RFC5245" /> are still in effect. The
introduced fairness might be better, but not worse than what
exists today.
</t>
</section>
<section anchor="notation" title="Notational Conventions">
<t>
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 <xref target="RFC2119"/>.
</t>
<t>
This document uses terminology defined in <xref
target="RFC5245"/>.
</t>
</section>
<section title="Improving ICE Multihomed Fairness">
<t>
A multihomed ICE agent can potentially send and receive
connectivity checks on all available interfaces and IP
addresses. It is possible for an interface to have several IP
addresses associated with it. To avoid unnecessary delay when
performing connectivity checks it would be beneficial to
prioritize interfaces and IP addresses known by the agent to
provide stable connectivity. If the agent have
access to information about the physical network it is
connected to (Like SSID in a WiFi Network) this can be used as
information regarding how that network interface should be
prioritized at this point in time.
</t>
<t>
The application knowledge regarding the reliability of an
interface can also be based on simple metrics like previous
connection success/failure rates or a more static model based
on interface types like wired, wireless, cellular, virtual,
tunneled and so on.
</t>
<t>
Candidates from a interface known to the application to
provide unreliable connectivity SHOULD get a low candidate
priority. This ensures they appear near the end of the
candidate list, and would be the last to be tested during the
connectivity check phase. This allows candidate pairs more
likely to succeed to be tested first.
</t>
<t>
If the application is unable to get any interface information
regarding type or unable to store any relevant metrics, it
SHOULD treat all interfaces as if they have reliable
connectivity. This ensures all interfaces gets their fair
chance to perform their connectivity checks.
</t>
</section>
<section title="Improving ICE Dual Stack Fairness">
<t>
Candidates SHOULD be prioritized such that a long sequence of
candidates belonging to the same address family will be
intermingled with candidates from an alternate IP family. For
example, promoting IPv4 candidates in the presence of many
IPv6 candidates such that an IPv4 address candidate is always
present after a small sequence of IPv6 candidates, i.e.,
reordering candidates such that both IPv6 and IPv4 candidates
get a fair chance during the connectivity check phase. This
makes ICE connectivity checks more responsive to broken path
failures of an address family.
</t>
<t>
An ICE agent can choose an algorithm or a technique of its
choice to ensure that the resulting check lists have a fair
intermingled mix of IPv4 and IPv6 address families. However,
modifying the check list directly can lead to uncoordinated
local and remote check lists that result in ICE taking longer
to complete or in the worst case scenario fail. The best
approach is to modify the formula for calculating the
candidate priority value described in ICE <xref
target="RFC5245"/> section 4.1.2.1.
</t>
<t>
Implementations SHOULD prioritize IPv6 candidates by putting
some of them first in the the intermingled checklist. This
increases the chance of a IPv6 connectivity checks to complete
first and be ready for nomination or usage. This enables
implementations to follow the intent of <xref
target="RFC6555"/> "Happy Eyeballs: Success with Dual-Stack
Hosts". It is worth noting that the timing recommendations in
<xref target="RFC6555"/> are to excessive for ICE usage.
</t>
</section>
<section anchor="compability" title="Compatibility">
<t>
ICE <xref target="RFC5245"/> section 4.1.2 states that the
formula in section 4.1.2.1 SHOULD be used to calculate the
candidate priority. The formula is as follows:
</t>
<t><figure>
<artwork align="left"><![CDATA[
priority = (2^24)*(type preference) +
(2^8)*(local preference) +
(2^0)*(256 - component ID)
]]></artwork>
</figure>
</t>
<t>
ICE <xref target="RFC5245"/> section 4.1.2.2 has guidelines
for how the type preference and local preference value should
be chosen. Instead of having a static local preference value
for IPv4 and IPv6 addresses, it is possible to choose this
value dynamically in such a way that IPv4 and IPv6 address
candidate priorities ends up intermingled within the same
candidate type. It is also possible to assign lower priorities
to IP addresses derived from unreliable interfaces using the
local preference value.
</t>
<t>
It is worth mentioning that <xref target="RFC5245"/> section
4.1.2 say that; "if there are multiple candidates for a
particular component for a particular media stream that have
the same type, the local preference MUST be unique for each
one".
</t>
<t>
The local type preference can be dynamically changed in such a
way that IPv4 and IPv6 address candidates end up intermingled
regardless of candidate type. This is useful if there are a
lot of IPv6 host candidates effectively blocking connectivity
checks for IPv4 server reflexive candidates.
</t>
<t>
Candidates with IP addresses from a unreliable interface SHOULD
be ordered at the end of the checklist. Not intermingled as the
dual-stack candidates.
</t>
<t>
The list below shows a sorted local candidate list where the
priority is calculated in such a way that the IPv4 and IPv6
candidates are intermingled (No multihomed candidates). To
allow for earlier connectivity checks for the IPv4 server
reflexive candidates, some of the IPv6 host candidates are
demoted. This is just an example of how a candidate priorities
can be calculated to provide better fairness between IPv4 and
IPv6 candidates without breaking any of the ICE connectivity
checks.
</t>
<t><figure>
<artwork align="left"><![CDATA[
Candidate Address Component
Type Type ID Priority
-------------------------------------------
(1) HOST IPv6 (1) 2129289471
(2) HOST IPv6 (2) 2129289470
(3) HOST IPv4 (1) 2129033471
(4) HOST IPv4 (2) 2129033470
(5) HOST IPv6 (1) 2128777471
(6) HOST IPv6 (2) 2128777470
(7) HOST IPv4 (1) 2128521471
(8) HOST IPv4 (2) 2128521470
(9) HOST IPv6 (1) 2127753471
(10) HOST IPv6 (2) 2127753470
(11) SRFLX IPv6 (1) 1693081855
(12) SRFLX IPv6 (2) 1693081854
(13) SRFLX IPv4 (1) 1692825855
(14) SRFLX IPv4 (2) 1692825854
(15) HOST IPv6 (1) 1692057855
(16) HOST IPv6 (2) 1692057854
(17) RELAY IPv6 (1) 15360255
(18) RELAY IPv6 (2) 15360254
(19) RELAY IPv4 (1) 15104255
(20) RELAY IPv4 (2) 15104254
SRFLX = server reflexive
]]></artwork>
</figure>
</t>
<t>
Note that the list does not alter the component ID part of the
formula. This keeps the different components (RTP and RTCP)
close in the list. What matters is the ordering of the
candidates with component ID 1. Once the checklist is formed
for a media stream the candidate pair with component ID 1 will
be tested first. If ICE connectivity check is successful then
other candidate pairs with the same foundation will be
unfrozen (<xref target="RFC5245"/> section 5.7.4. Computing
States).
</t>
<t>
The local and remote agent can have different algorithms for
choosing the local preference and type preference values
without impacting the synchronization between the local and
remote check lists.
</t>
<t>
The check list is made up by candidate pairs. A candidate pair
is two candidates paired up and given a candidate pair
priority as described in <xref target="RFC5245"/> section
5.7.2. Using the pair priority formula:
</t>
<t>
<figure>
<artwork align="left"><![CDATA[
pair priority = 2^32*MIN(G,D) + 2*MAX(G,D) + (G>D?1:0)
]]></artwork>
</figure>
</t>
<t>
Where G is the candidate priority provided by the controlling
agent and D the candidate priority provided by the controlled
agent. This ensures that the local and remote check lists are
coordinated.
</t>
<t>
Even if the two agents have different algorithms for choosing
the candidate priority value to get an intermingled set of
IPv4 and IPv6 candidates, the resulting checklist, that is a
list sorted by the pair priority value, will be identical on
the two agents.
</t>
<t>
The agent that has promoted IPv4 cautiously i.e. lower IPv4
candidate priority values compared to the other agent, will
influence the check list the most due to (2^32*MIN(G,D)) in
the formula.
</t>
<t>
These recommendations are backward compatible with a standard
ICE implementation. The resulting local and remote checklist
will still be synchronized. The introduced fairness might be
better, but not worse than what exists today
</t>
<t>
If aggressive nomination is in use the procedures described in
this document might change what candidate pair ends up as the
active one.
</t>
<t>
A test implementation with an example algorithm is available
<xref target="ICE_dualstack_imp"/>.
</t>
</section>
<section title="IANA Considerations">
<t>
None.
</t>
</section>
<section title="Implementation Status">
<t>
[Note to RFC Editor: Please remove this section and reference to
<xref target="RFC6982"></xref> prior to publication.]
</t>
<t>
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in <xref
target="RFC6982"></xref>. The description of implementations in this
section is intended to assist the IETF in its decision processes in
progressing drafts to RFCs. Please note that the listing of any
individual implementation here does not imply endorsement by the IETF.
Furthermore, no effort has been spent to verify the information
presented here that was supplied by IETF contributors. This is not
intended as, and must not be construed to be, a catalog of available
implementations or their features. Readers are advised to note that
other implementations may exist.
</t>
<t>
According to <xref target="RFC6982"></xref>, "this will allow
reviewers and working groups to assign due consideration to documents
that have the benefit of running code, which may serve as evidence of
valuable experimentation and feedback that have made the implemented
protocols more mature. It is up to the individual working groups to use
this information as they see fit".
</t>
<section title="ICE-Dual Starck Fairness Test code">
<t>
<list style="hanging">
<t hangText="Organization: ">Cisco
</t>
<t hangText="Description: ">
Open-Source ICE, TURN and STUN implementation.
</t>
<t hangText="Implementation: ">
https://github.com/palerikm/ICE-DualStackFairness
</t>
<t hangText="Level of maturity: ">
Code is stable. Tests
</t>
<t hangText="Coverage: ">
Follows the recommendations in this document
</t>
<t hangText="Licensing: ">
BSD
</t>
<t hangText="Implementation experience: ">
Straightforward as there are no compatibility issues.
</t>
<t hangText="Contact: ">
Paal-Erik Martinsen
</t>
</list>
</t>
</section>
<section title="ICE-Dual Starck Fairness Test code">
<t>
<list style="hanging">
<t hangText="Organization: ">Others
</t>
<t hangText="Description: ">
Major ICE implementations, browser based and stand-alone ICE, TURN and STUN implementations.
</t>
<t hangText="Implementation: ">
Product specific.
</t>
<t hangText="Level of maturity: ">
Code is stable and available in the wild.
</t>
<t hangText="Coverage: ">
Implements the recommendations in this document.
</t>
<t hangText="Licensing: ">
Some open source, some close source
</t>
<t hangText="Implementation experience: ">
Already implemented in some of the implementations. This
documents describes what needs to be done to achieve the
desired fairness.
</t>
</list>
</t>
</section>
</section>
<section anchor="security" title="Security Considerations">
<t>
STUN connectivity check using MAC computed during key
exchanged in the signaling channel provides message integrity
and data origin authentication as described in section 2.5 of
<xref target="RFC5245"/> apply to this use.
</t>
</section>
<section anchor="ack" title="Acknowledgements">
<t>
Authors would like to thank Dan Wing, Ari Keranen, Bernard
Aboba, Martin Thomson, Jonathan Lennox, Balint Menyhart, Ole
Troan and Simon Perreault for their comments and review.
</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.RFC.3484"?>
<?rfc include="reference.RFC.5245"?>
<?rfc include="reference.RFC.6555"?>
<?rfc include="reference.RFC.6724"?>
<?rfc include="reference.RFC.6982"?>
</references>
<references title="Informative References">
<reference anchor="ICE_dualstack_imp" target="https://github.com/palerikm/ICE-DualStackFairness">
<front>
<title>ICE DualStack Test Implementation github repo</title>
<author fullname="Paal-Erik Martinsen" initials="P.E" surname="Martinsen">
<organization abbrev="Cisco">Cisco Systems, Inc.</organization>
<address>
<postal>
<street>Philip Pedersens Vei 22</street>
<city>Lysaker</city>
<region>Akershus</region>
<code>1325</code>
<country>Norway</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<date/>
</front>
</reference>
</references>
</back>
</rfc>