ICE P. Martinsen Internet-Draft T. Reddy Intended status: Best Current Practice P. Patil Expires: February 5, 2017 Cisco August 4, 2016 ICE Multihomed and IPv4/IPv6 Dual Stack Fairness draft-ietf-ice-dualstack-fairness-04 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 February 5, 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 Martinsen, et al. Expires February 5, 2017 [Page 1] Internet-Draft ICE Multihomed and DualStack Fairness August 2016 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 . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . 9 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 more fairness when handling 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 Martinsen, et al. Expires February 5, 2017 [Page 2] Internet-Draft ICE Multihomed and DualStack Fairness August 2016 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 excessively 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. 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. If an agent supporting the guidelines in this specification talks to an "old" ICE agent, the introduced fairness might be better, but not worse than what exists today. 2. Notational Conventions This document uses terminology defined in [I-D.ietf-ice-rfc5245bis]. 3. Improving ICE Multihomed Fairness 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 has 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. Martinsen, et al. Expires February 5, 2017 [Page 3] Internet-Draft ICE Multihomed and DualStack Fairness August 2016 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 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. 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 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 modify 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] are not optimal for ICE usage. Martinsen, et al. Expires February 5, 2017 [Page 4] Internet-Draft ICE Multihomed and DualStack Fairness August 2016 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. 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. Martinsen, et al. Expires February 5, 2017 [Page 5] Internet-Draft ICE Multihomed and DualStack Fairness August 2016 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 ([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) Martinsen, et al. Expires February 5, 2017 [Page 6] Internet-Draft ICE Multihomed and DualStack Fairness August 2016 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 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.] 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. Martinsen, et al. Expires February 5, 2017 [Page 7] Internet-Draft ICE Multihomed and DualStack Fairness August 2016 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. 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. Martinsen, et al. Expires February 5, 2017 [Page 8] Internet-Draft ICE Multihomed and DualStack Fairness August 2016 8. Security Considerations The security considerations described in [I-D.ietf-ice-rfc5245bis] are still valid. This specification does not add or remove any security considerations. It changes recommended values and describes how an agent could choose those values in a safe way. 9. Acknowledgements 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. 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-04 (work in progress), June 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, . [RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with Dual-Stack Hosts", RFC 6555, DOI 10.17487/RFC6555, April 2012, . [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, . [RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", RFC 6982, DOI 10.17487/RFC6982, July 2013, . 10.2. Informative References Martinsen, et al. Expires February 5, 2017 [Page 9] Internet-Draft ICE Multihomed and DualStack Fairness August 2016 [ICE_dualstack_imp] Martinsen, P., "ICE DualStack Test Implementation github repo", . 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 Martinsen, et al. Expires February 5, 2017 [Page 10]