Internet DRAFT - draft-martinsen-mmusic-ice-dualstack-fairness
draft-martinsen-mmusic-ice-dualstack-fairness
MMUSIC P. Martinsen
Internet-Draft T. Reddy
Intended status: Standards Track P. Patil
Expires: August 13, 2015 Cisco
February 9, 2015
ICE IPv4/IPv6 Dual Stack Fairness
draft-martinsen-mmusic-ice-dualstack-fairness-02
Abstract
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on August 13, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3
3. Improving ICE Multihomed Fairness . . . . . . . . . . . . . . 3
4. Improving ICE Dual Stack Fairness . . . . . . . . . . . . . . 3
5. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Example Algorithm for Choosing the Local Preference . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. Normative References . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Applications should take special care to deprioritize network
interfaces known to provide unreliable connectivity. For example
certain tunnel services might provide unreliable connectivity. The
simple guidelines presented here describes how to deprioritize
interfaces known by the application to provide unreliable
connectivity. This application knowledge can 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, tunnelled and so on.
There is a also need to introduce more fairness in the handling of
connectivity checks for different IP address families in dual-stack
IPv4/IPv6 ICE scenarios. Section 4.1.2.1 of ICE [RFC5245] points to
[RFC3484] for prioritizing among the different IP families.
[RFC3484] is obsoleted by [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.
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.
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The cost is a small penalty to the address type that otherwise would
have been prioritized.
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 [RFC5245] are still in effect. The
introduced fairness might be better, but not worse than what exists
today.
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].
This document uses terminology defined in [RFC5245].
3. Improving ICE Multihomed Fairness
A multihomed ICE agent can potentially send and receive connectivity
checks on all available interfaces. To avoid unnecessary delay when
performing connectivity checks it would be beneficial to prioritize
interfaces known by the agent to provide connectivity.
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.
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.
4. Improving ICE Dual Stack Fairness
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.
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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 [RFC5245] section 4.1.2.1.
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 [RFC6555]Happy Eyeballs: Success with Dual-Stack Hosts.
5. Compatibility
ICE [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:
priority = (2^24)*(type preference) +
(2^8)*(local preference) +
(2^0)*(256 - component ID)
ICE [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 dynamically change the type preference 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.
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. 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.
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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
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 ([RFC5245] section 5.7.4. Computing
States).
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.
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 [RFC5245] section 5.7.2. Using the pair priority
formula:
pair priority = 2^32*MIN(G,D) + 2*MAX(G,D) + (G>D?1:0)
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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.
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.
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.
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
6. Example Algorithm for Choosing the Local Preference
The algorithm described in this section can be used by an
implementation to introduce IPv4/IPv6 dual stack and multihomed
fairness. Implementations implementing their own algorithm must take
care not to break any ICE compatibility. See Section Section 5 for
details.
The value space for the local preference is from 0 to 65535
inclusive. This value space can be divided up in chunks for each IP
address family.
An IPv6 and IPv4 start priority must be given. In this example IPv6
starts at 60000 and IPv4 at 59000. IPv6 should be given the highest
start priority.
Interfaces known to the application to provide unreliable
connectivity will be given a low local_preference value. This will
place candidates from those interface near the end in a sorted
candidate list.
IPv6 IPv4
Start Start
65535 60k 59k 58k 57k 56k 55k 0
+--------+------+------+------+------+------+---------------------+
| | IPv6 | IPv4 | IPv6 | IPv4 | IPv6 | |
| | (1) | (1) | (2) | (2) | (3) | |
+--------+------+------+------+------+------+---------------------+
<- N->
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The local preference can be calculated by the given formula:
local_preference = ((S - N*2*(Cn/Cmax))* Ri) + I
S: Address type specific start value (IPv4 or IPv6 Start)
N: Absolute value of IPv6_start-IPv4_start. This ensures a positive
number even if IPv4 is the highest priority.
Cn: Number of current candidates of a specific IP address type and
candidate type (host, server reflexive or relay).
Cmax: Number of allowed consecutive candidates of the same IP
address type.
Ri: Reliable interface. A reliable interface known by the
application to provide reliable connectivity should set this value
to 1. Interfaces known to provide unreliable connectivity should
set this to 0. (Allowed values are 0 and 1)
I: Interface priority. Unreliable interfaces can set this value to
get a priority among the unreliable interfaces. Max value is
recommended to be N. Reliable interfaces should set this to 0.
Using the values N=abs(60000-59000) and Cmax = 2 yields the following
sorted local candidate list with only reliable interfaces:
(1) HOST IPv6 (1) Priority: 2129289471
(2) HOST IPv6 (2) Priority: 2129289470
(3) HOST IPv4 (1) Priority: 2129033471
(4) HOST IPv4 (2) Priority: 2129033470
(5) HOST IPv6 (1) Priority: 2128777471
(6) HOST IPv6 (2) Priority: 2128777470
(7) HOST IPv4 (1) Priority: 2128521471
(8) HOST IPv4 (2) Priority: 2128521470
(9) HOST IPv6 (1) Priority: 2128265471
(10) HOST IPv6 (2) Priority: 2128265470
(11) SRFLX IPv6 (1) Priority: 1693081855
(12) SRFLX IPv6 (2) Priority: 1693081854
(13) SRFLX IPv4 (1) Priority: 1692825855
(14) SRFLX IPv4 (2) Priority: 1692825854
(15) RELAY IPv6 (1) Priority: 15360255
(16) RELAY IPv6 (2) Priority: 15360254
(17) RELAY IPv4 (1) Priority: 15104255
(18) RELAY IPv4 (2) Priority: 15104254
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The result is an even spread of IPv6 and IPv4 candidates among the
different candidate types (host, server reflexive, relay). The local
preference value is calculated separately for each candidate type.
7. IANA Considerations
None.
8. Security Considerations
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 [RFC5245] apply to this
use.
9. Acknowledgements
Authors would like to thank Dan Wing, Ari Keranen, Bernard Aboba,
Martin Thomson, Jonathan Lennox, Balint Menyhart and Simon Perreault
for their comments and review.
10. 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.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245, April
2010.
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, April 2012.
[RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, September 2012.
Authors' Addresses
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Paal-Erik Martinsen
Cisco Systems, Inc.
Philip Pedersens Vei 22
Lysaker, Akershus 1325
Norway
Email: palmarti@cisco.com
Tirumaleswar Reddy
Cisco Systems, Inc.
Cessna Business Park, Varthur Hobli
Sarjapur Marathalli Outer Ring Road
Bangalore, Karnataka 560103
India
Email: tireddy@cisco.com
Prashanth Patil
Cisco Systems, Inc.
Bangalore
India
Email: praspati@cisco.com
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