Internet DRAFT - draft-ietf-ice-dualstack-fairness
draft-ietf-ice-dualstack-fairness
ICE P. Martinsen
Internet-Draft T. Reddy
Intended status: Best Current Practice P. Patil
Expires: May 18, 2017 Cisco
November 14, 2016
ICE Multihomed and IPv4/IPv6 Dual Stack Guidelines
draft-ietf-ice-dualstack-fairness-07
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
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
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 18, 2017.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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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. ICE Multihomed Recomendations . . . . . . . . . . . . . . . . 3
4. ICE Dual Stack Recomendations . . . . . . . . . . . . . . . . 4
5. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 7
7.1. ICE-Dual Stack Fairness Test code . . . . . . . . . . . . 8
7.2. ICE-Dual Stack Fairness Test code . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
In multihomed and IPv4/IPv6 dual-stack environments ICE
[I-D.ietf-ice-rfc5245bis] would benefit by a fair distribution of its
connectivity checks across available interfaces or IP address types.
With a fair distribution of the connectivity checks, excessive delays
are avoided if a particular network path is broken or slow. It would
arguably be better to put the interfaces or address types known to
the application last in the checklist. However, the main motivation
by ICE is to make no assumptions regarding network topology, hence a
fair distribution of the connectivity checks is more appropriate. If
an application operates in a well-known environment is can safely
override the recommendation given in this document.
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
describe how to deprioritize interfaces known by the application to
provide unreliable connectivity.
There is also a need to introduce better handling of connectivity
checks for different IP address families in dual-stack IPv4/IPv6 ICE
scenarios. Following the recommendations from RFC6724 [RFC6724] will
lead to prioritization of IPv6 over IPv4 for the same candidate type.
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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 user noticeable delays when either IPv6 or IPv4 path is
broken or excessively slow, this specification encourages
intermingling the different address families when connectivity checks
are performed. This 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. Further this document recommends to keep
track of previous known connectivity problem and assign a lower
priority to those addresses. Specific mechanisms and rules for
tracking connectivity issues are out of scope for this document.
This document describes what parameters an agent can safely alter to
fairly order the checklist candidate pairs in multihomed and dual-
stack environments, thus affecting the sending order of the
connectivity checks. Actual values of those parameters is an
implementation detail. Dependant on the nomination method in use,
this might 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.
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] and ICEbis
[I-D.ietf-ice-rfc5245bis] are still in effect.
2. Notational Conventions
This document uses terminology defined in [I-D.ietf-ice-rfc5245bis].
3. ICE Multihomed Recomendations
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.
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
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wired, wireless, cellular, virtual, tunneled in conjunction with
other operational metrics. This would require the application to
have the right permissions to obtain such operational metrics.
Candidates from an interface known to the application to provide
unreliable connectivity should get a low candidate priority. When to
consider connectivity as unreliable is implementation specific.
Usage of ICE is not limited to VoIP applications. What an
application sees as unreliability might be determined by a mix of how
long lived the connection is, how often setup is required and others,
for now unknown, requirements. This is purely an optimization to
speed up the ICE connectivity check phase.
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. ICE Dual Stack Recomendations
Candidates should be prioritized such that a 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.
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 set the appropriate value for local
preference in the formula for calculating the candidate priority
value described in ICE [I-D.ietf-ice-rfc5245bis] section "4.1.2.1
Recommended Formula".
Implementations should prioritize IPv6 candidates by putting some of
them first in the intermingled checklist. This increases the chance
of 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".
It is worth noting that the timing recommendations in [RFC6555] will
be overruled by how ICE paces out its connectivity checks.
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A simple formula to calculate how many IPv6 addresses to put before
any IPv4 addresses could look like:
Hi = (N_4 + N_6) / N_4
Where Hi = Head start before intermingling starts
N_4 = Number of IPv4 addresses
N_6 = Number of IPv6 addresses
If a host have 2 IPv4 addresses and 6 IPv6 addresses, it will insert
an IP4 address after 4 IPv6 addresses by choosing the appropriate
local preference values when calculating the pair priorities.
5. Compatibility
ICE [I-D.ietf-ice-rfc5245bis] section "4.1.2 Prioritizing Candidates"
states that the formula in section "4.1.2.1 Recommended Formula"
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 [I-D.ietf-ice-rfc5245bis] section "4.1.2.2 Guidelines for
Choosing Type and Local Preferences" 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 end 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.
It is worth mentioning that [I-D.ietf-ice-rfc5245bis] section
"4.1.2.1 Recommended Formula" says that; "if there are multiple
candidates for a particular component for a particular media stream
that has the same type, the local preference MUST be unique for each
one".
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.
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Candidates with IP addresses from an unreliable interface should be
ordered at the end of the checklist, i.e., not intermingled as the
dual-stack 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 (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.
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
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same foundation will be unfrozen ([I-D.ietf-ice-rfc5245bis] section
5.1.3.4. 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 of candidate pairs. A candidate pair is
two candidates paired up and given a candidate pair priority as
described in [I-D.ietf-ice-rfc5245bis] section 5.1.3.2. Using the
pair priority formula:
pair priority = 2^32*MIN(G,D) + 2*MAX(G,D) + (G>D?1:0)
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.
Dependant of the nomination method in use the procedures described in
this document might change what candidate pair ends up as the active
one.
A test implementation of an example algorithm is available at
[ICE_dualstack_imp].
6. IANA Considerations
None.
7. Implementation Status
[Note to RFC Editor: Please remove this section and reference to
[RFC6982] prior to publication.]
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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 [RFC6982].
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.
According to [RFC6982], "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".
7.1. ICE-Dual Stack Fairness Test code
Organization: Cisco
Description: Open-Source ICE, TURN and STUN implementation.
Implementation: https://github.com/palerikm/ICE-DualStackFairness
Level of maturity: Code is stable.
Coverage: Follows the recommendations in this document
Licensing: BSD
Implementation experience: Straightforward as there are no
compatibility issues.
Contact: Paal-Erik Martinsen palmarti@cisco.com
7.2. ICE-Dual Stack Fairness Test code
Organization: Others
Description: Major ICE implementations, browser based and stand-
alone ICE, TURN and STUN implementations.
Implementation: Product specific.
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Level of maturity: Code is stable and available in the wild.
Coverage: Implements the recommendations in this document.
Licensing: Some open source, some close source
Implementation experience: Already implemented in some of the
implementations. This document describes what needs to be done to
achieve the desired fairness.
8. Security Considerations
The security considerations described in [I-D.ietf-ice-rfc5245bis]
are still valid. It changes recommended values and describes how an
agent could choose those values in a safe way. In section Section 3
the agent can prioritize the network interface based on previous
network knowledge. This can potentially be unwanted information
leakage towards the remote agent.
9. Acknowledgements
Authors would like to thank Dan Wing, Ari Keranen, Bernard Aboba,
Martin Thomson, Jonathan Lennox, Balint Menyhart, Ole Troan, Simon
Perreault, Ben Cambell and Mirja Kuehlewind for their comments and
review.
10. References
10.1. Normative References
[I-D.ietf-ice-rfc5245bis]
Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", draft-ietf-ice-
rfc5245bis-05 (work in progress), October 2016.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245, DOI
10.17487/RFC5245, April 2010,
<http://www.rfc-editor.org/info/rfc5245>.
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, DOI 10.17487/RFC6555, April
2012, <http://www.rfc-editor.org/info/rfc6555>.
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[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
<http://www.rfc-editor.org/info/rfc6724>.
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", RFC 6982, DOI
10.17487/RFC6982, July 2013,
<http://www.rfc-editor.org/info/rfc6982>.
10.2. Informative References
[ICE_dualstack_imp]
Martinsen, P., "ICE DualStack Test Implementation github
repo", <https://github.com/palerikm/ICE-
DualStackFairness>.
Authors' Addresses
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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