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Internet Engineering Task Force (IETF)                       S. KrishnanRequest for Comments: 8319                                        KaloomUpdates:4861                                                J. KorhonenCategory: Standards Track                       Nordic Semiconductor ASAISSN: 2070-1721                                           S. Chakrabarti                                                                 Verizon                                                             E. Nordmark                                                                  Zededa                                                          A. Yourtchenko                                                                   Cisco                                                           February 2018Support for Adjustable Maximum Router Lifetimes per LinkAbstract   The IPv6 Neighbor Discovery protocol specifies the maximum time   allowed between sending unsolicited multicast Router Advertisements   (RAs) from a router interface as well as the maximum router lifetime.   It also allows the limits to be overridden by documents that are   specific to the link layer.  This document allows for overriding   these values on a per-link basis.   This document specifies updates to the IPv6 Neighbor Discovery   Protocol (RFC 4861) to increase the maximum time allowed between   sending unsolicited multicast RAs from a router interface as well as   to increase the maximum router lifetime.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttps://www.rfc-editor.org/info/rfc8319.Krishnan, et al.             Standards Track                    [Page 1]

RFC 8319               Adjustable Router Lifetimes         February 2018Copyright Notice   Copyright (c) 2018 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (https://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 Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .32.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .3   3.  Relationship between AdvDefaultLifetime and MaxRtrAdvInterval   34.  Updates toRFC 4861 . . . . . . . . . . . . . . . . . . . . .45.  Host Behavior . . . . . . . . . . . . . . . . . . . . . . . .56.  Security Considerations . . . . . . . . . . . . . . . . . . .57.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .58.  References  . . . . . . . . . . . . . . . . . . . . . . . . .58.1.  Normative References  . . . . . . . . . . . . . . . . . .58.2.  Informative References  . . . . . . . . . . . . . . . . .6   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .6   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .7Krishnan, et al.             Standards Track                    [Page 2]

RFC 8319               Adjustable Router Lifetimes         February 20181.  Introduction   IPv6 Neighbor Discovery relies on IP multicast based on the   expectation that multicast makes efficient use of available bandwidth   and avoids generating interrupts in the network nodes.  On some data   link layers, multicast may not be natively supported.  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 clarifications specific to   the link technology about how to tune the Neighbor Discovery Protocol   (NDP) constants for certain systems in order to reduce excess NDP   traffic.  For example, [RFC6459] and [RFC7066] contain such   clarifications for 3GPP cellular links.   This document specifies updates to the IPv6 Neighbor Discovery   Protocol [RFC4861] to increase the maximum time allowed between   sending unsolicited multicast RAs from a router interface as well as   to increase the maximum router lifetime.2.  Requirements Language   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and   "OPTIONAL" in this document are to be interpreted as described inBCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all   capitals, as shown here.3.  Relationship between AdvDefaultLifetime and MaxRtrAdvInterval   MaxRtrAdvInterval is an upper bound on the time between which two   successive Router Advertisement messages are sent.  Therefore, one   might reason about the relationship between these two values in terms   of a ratio K = AdvDefaultLifetime / MaxRtrAdvInterval, which   expresses how many Router Advertisements are guaranteed to be sent   before the router lifetime expires.   Assuming unicast Solicited Router Advertisements or a perfectly   stable network, on a theoretically perfect link with no losses, it   would be 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 that 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.Krishnan, et al.             Standards Track                    [Page 3]

RFC 8319               Adjustable Router Lifetimes         February 2018   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% 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 -- which should be good enough for a lot of   scenarios.   In a network with higher packet loss probabilities or if 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 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 according 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.4.  Updates toRFC 4861   This document updates Sections4.2 and6.2.1 of [RFC4861] to change   the following router configuration variables.   InSection 4.2, inside the paragraph that defines Router Lifetime,   change 9000 to 65535 seconds.   InSection 6.2.1, inside the paragraph that defines   MaxRtrAdvInterval, change 1800 to 65535 seconds.   InSection 6.2.1, inside the paragraph that defines   AdvDefaultLifetime, change 9000 to 65535 seconds.   As explained inSection 3, the probability of packet loss must be   considered when choosing the relationship between MaxRtrAdvInterval   and AdvDefaultLifetime.Krishnan, et al.             Standards Track                    [Page 4]

RFC 8319               Adjustable Router Lifetimes         February 20185.  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 issue with setting this field   to more than 9000, but there might be implementations that   incorrectly reject such RAs (sinceRFC 4861 requires receivers to   handle any value).6.  Security Considerations   On a link where Router Advertisements are few and far between, the   detrimental effects of a rogue router that sends an unsolicited RA   are greatly increased.  These rogue RAs can be prevented by using   approaches like RA-Guard [RFC6105] and SEcure Neighbor Discovery   (SEND) [RFC3971].7.  IANA Considerations   This document has no IANA actions.8.  References8.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <https://www.rfc-editor.org/info/rfc2119>.   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,              "Neighbor Discovery for IP version 6 (IPv6)",RFC 4861,              DOI 10.17487/RFC4861, September 2007,              <https://www.rfc-editor.org/info/rfc4861>.   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase inRFC 2119 Key Words",BCP 14,RFC 8174,              DOI 10.17487/RFC8174, May 2017,              <https://www.rfc-editor.org/info/rfc8174>.Krishnan, et al.             Standards Track                    [Page 5]

RFC 8319               Adjustable Router Lifetimes         February 20188.2.  Informative References   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,              "SEcure Neighbor Discovery (SEND)",RFC 3971,              DOI 10.17487/RFC3971, March 2005,              <https://www.rfc-editor.org/info/rfc3971>.   [RFC6105]  Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.              Mohacsi, "IPv6 Router Advertisement Guard",RFC 6105,              DOI 10.17487/RFC6105, February 2011,              <https://www.rfc-editor.org/info/rfc6105>.   [RFC6459]  Korhonen, J., Ed., Soininen, J., Patil, B., Savolainen,              T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation              Partnership Project (3GPP) Evolved Packet System (EPS)",RFC 6459, DOI 10.17487/RFC6459, January 2012,              <https://www.rfc-editor.org/info/rfc6459>.   [RFC7066]  Korhonen, J., Ed., Arkko, J., Ed., Savolainen, T., and S.              Krishnan, "IPv6 for Third Generation Partnership Project              (3GPP) Cellular Hosts",RFC 7066, DOI 10.17487/RFC7066,              November 2013, <https://www.rfc-editor.org/info/rfc7066>.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   document.  The authors would also like to thank Lorenzo Colitti, Erik   Kline, Jeena Rachel John, Brian Carpenter, Tim Chown, Fernando Gont,   Warren Kumari, and Adam Roach for their comments and suggestions that   improved this document.Krishnan, et al.             Standards Track                    [Page 6]

RFC 8319               Adjustable Router Lifetimes         February 2018Authors' Addresses   Suresh Krishnan   Kaloom   335 Rue Peel   Montreal, QC   Canada   Email: suresh@kaloom.com   Jouni Korhonen   Nordic Semiconductor ASA   Metsanneidonkuja 10   02130 Espoo   Finland   Email: jouni.nospam@gmail.com   Samita Chakrabarti   Verizon   United States of America   Email: samita.chakrabarti@verizon.com   Erik Nordmark   Zededa   Santa Clara, CA   United States of America   Email: nordmark@acm.org   Andrew Yourtchenko   Cisco   6b de Kleetlaan   Diegem  1831   Belgium   Email: ayourtch@cisco.comKrishnan, et al.             Standards Track                    [Page 7]