| MMUSIC | T. Reddy |
| Internet-Draft | P. Patil |
| Intended status: Standards Track | P. Martinsen |
| Expires: January 1, 2015 | Cisco |
| June 30, 2014 |
Happy Eyeballs Extension for ICE
draft-reddy-mmusic-ice-happy-eyeballs-07
This document provides guidelines on how to make Interactive Connectivity Establishment (ICE) conclude faster in IPv4/IPv6 dual-stack scenarios where broken paths exist. The provided guidelines are backwards compatible with the original ICE specification.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
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There is a 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. 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.
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].
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.
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. 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.
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 was 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) 212928947
(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)
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
None.
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.
Authors would like to thank Dan Wing, Ari Keranen, Bernard Aboba, Martin Thomson, Jonathan Lennox and Balint Menyhart for their comments and review.
| [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. |
| [RFC6724] | Thaler, D., Draves, R., Matsumoto, A. and T. Chown, "Default Address Selection for Internet Protocol Version 6 (IPv6)", RFC 6724, September 2012. |
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. This leaves enough address space to further play with the values if different interface priorities needs to be added. The highest value should be given to the address family that should be prioritized.
IPv6 IPv4
Start Start
65535 60k 59k 58k 57k 56k 55k 0
+--------+------+------+------+------+------+---------------------+
| | IPv6 | IPv4 | IPv6 | IPv4 | IPv6 | |
| | (1) | (1) | (2) | (2) | (3) | |
+--------+------+------+------+------+------+---------------------+
<- N->
The local preference can be calculated by the given formula:
local_preference = S - N*2*(Cn/Cmax)
(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
Using the values N=abs(60000-59000) and Cmax = 2 yields the following sorted local candidate list: