IPv6 Maintenance S. Krishnan Internet-Draft Ericsson Updates: 4861 (if approved) J. Korhonen Intended status: Standards Track Broadcom Expires: January 7, 2016 S. Chakrabarti Ericsson E. Nordmark Arista Networks A. Yourtchenko cisco July 6, 2015 Support for adjustable maximum router lifetimes per-link draft-krishnan-6man-maxra-02 Abstract The neighbor discovery protocol specifies the maximum time allowed between sending unsolicited multicast Router Advertisements from a router interface as well as the maximum router lifetime. It also allows the limits to be overridden by link-layer specific documents. This document allows for overriding these values on a per-link basis. 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 January 7, 2016. Copyright Notice Copyright (c) 2015 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 Krishnan, et al. Expires January 7, 2016 [Page 1] Internet-Draft Adjustable Router Lifetimes July 2015 (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 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Relationship between AdvDefaultLifetime and MaxRtrAdvInterval 3 4. Updates to RFC4861 . . . . . . . . . . . . . . . . . . . . . 4 5. Host Behavior . . . . . . . . . . . . . . . . . . . . . . . . 4 6. Security Considerations . . . . . . . . . . . . . . . . . . . 4 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 9.1. Normative References . . . . . . . . . . . . . . . . . . 5 9.2. Informative References . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction IPv6 Neighbor Discovery relies on IP multicast with the expectation to be efficient with respect to available bandwidth and to avoid generating interrupts in the network nodes. On some datalink-layer network, for example IEEE 802.11 WiFi, this is not the case because of limitations in the services offered by the datalink-layer network [draft-vyncke-6man-mcast-not-efficient-01]. On such links any possible reduction of multicast traffic will be highly beneficial. Unfortunately, due to the fixed protocol constants specified in [RFC4861] it is difficult to relax the multicast timers for neighbor discovery. There are already link technology specific clarifications how to tune protocol constants for certain system with the expectation to reduce excess Neighbor Discovery Protocol (NDP) traffic. 3GPP cellular links are one existing example [RFC6459][RFC7066]. This document specifies updates to the IPv6 Neighbor Discovery Protocol [RFC4861] for relaxing the the maximum time allowed between sending unsolicited multicast Router Advertisements (RA) from a router interface as well as for the maximum router lifetime. 2. Terminology Krishnan, et al. Expires January 7, 2016 [Page 2] Internet-Draft Adjustable Router Lifetimes July 2015 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]. 3. Relationship between AdvDefaultLifetime and MaxRtrAdvInterval MaxRtrAdvInterval is an upper bound on the time between the two successive Router Advertisement messages are sent, therefore one might reason about the relationship between these two values in terms of the ratio K=AdvDefaultLifetime/MaxRtrAdvInterval, which expresses how many Router Advertisements will be guaranteed to be sent before the router lifetime expiry. Assuming unicast Solicited Router Advertisements or a perfectly stable network, on a theoretically perfect link with no losses, it would have been sufficient to have K just above 1 - so that the sent Router Advertisement refreshes the router entry just before it expires. On the real links which allow for some loss, one would need to use K>2 in order to minimize the chances of a single router advertisement loss causing a loss of the router entry. The exact calculation will depend on the packet loss probability. An example: if we take a ballpark value of 1% probability of a packet loss, then K=2 will give 0.01% percent chance of an outage due to a packet loss, K=3 will give 0.0001% chance of an outage, and so forth. To reverse the numbers, with these parameters, K~=1 gives 99% reliability, K~=2 gives 99.99% reliability, and K~=3 gives 99.9999% reliability - the latter should be good enough for a lot of scenarios. In a network with higher packet loss or if the higher reliability is desired, the K might be chosen to be even higher. On the other hand, some of the data link layers provide reliable delivery at layer 2 - so there one might even consider using the "theoretical" value of K just above 1. Since the choice of these two parameters does not impact the interoperability per se, this document does not impose any specific constraints on their values other than providing the guidelines in this section, therefore each individual link can optimize accordingly to its use case. Also AdvDefaultLifetime MUST be set to a value greater than or equal to the selected MaxRtrAdvInterval. Otherwise, a router lifetime is guaranteed to expire before the new Router Advertisement has a chance to be sent, thereby creating an outage. Krishnan, et al. Expires January 7, 2016 [Page 3] Internet-Draft Adjustable Router Lifetimes July 2015 4. Updates to RFC4861 This document updates Section 6.2.1. of [RFC4861] to update the following router configuration variables. MaxRtrAdvInterval MUST be no greater than 21845. AdvDefaultLifetime MUST be between MaxRtrAdvInterval and 65535. This document also updates Sections 6.2.1., 6.2.2., 6.2.4. and 6.2.5. of [RFC4861] so that AdvSendAdvertisements can be set "FALSE" but the router would still continue be a router and respond with RAs to solicited RSes . 5. Host Behavior Legacy hosts on a link with updated routers may have issues with a Router Lifetime of more than 9000 seconds. In the few implementations we have tested with general purpose operating systems, there does not seem to be any issues with setting this field to more than 9000, but there might be implementations that incorrectly (since RFC4861 requires receivers to handle any value) reject such RAs. 6. Security Considerations On a link where router advertisements are few and far between, the attack window for a rogue router to send an unsolicited RA is greatly increased. These attacks can easily be prevented by using SeND [RFC3971] 7. IANA Considerations This document does not require any IANA action. 8. Acknowledgements The authors would like to thank the members of the 6man efficient ND design team for their comments that led to the creation of this draft. The authors would also like to thank Lorenzo Colitti, Erik Kline and Jeena Rachel John for their comments and suggestions that improved this document. 9. References Krishnan, et al. Expires January 7, 2016 [Page 4] Internet-Draft Adjustable Router Lifetimes July 2015 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007. 9.2. Informative References [RFC6459] Korhonen, J., Soininen, J., Patil, B., Savolainen, T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation Partnership Project (3GPP) Evolved Packet System (EPS)", RFC 6459, January 2012. [RFC7066] Korhonen, J., Arkko, J., Savolainen, T., and S. Krishnan, "IPv6 for Third Generation Partnership Project (3GPP) Cellular Hosts", RFC 7066, November 2013. Authors' Addresses Suresh Krishnan Ericsson 8400 Decarie Blvd. Town of Mount Royal, QC Canada Phone: +1 514 345 7900 x42871 Email: suresh.krishnan@ericsson.com Jouni Korhonen Broadcom Porkkalankatu 24 FIN-00180 Helsinki Finland Email: jouni.nospam@gmail.com Krishnan, et al. Expires January 7, 2016 [Page 5] Internet-Draft Adjustable Router Lifetimes July 2015 Samita Chakrabarti Ericsson USA Email: samita.chakrabarti@ericsson.com Erik Nordmark Arista Networks Santa Clara, CA USA Email: nordmark@acm.org Andrew Yourtchenko cisco 6b de Kleetlaan Diegem 1831 Belgium Email: ayourtch@cisco.com Krishnan, et al. Expires January 7, 2016 [Page 6]