IPv6 Maintenance                                             S. Krishnan
Internet-Draft                                                    Kaloom
Updates: 4861 (if approved)                                  J. Korhonen
Intended status: Standards Track                                Broadcom
Expires: January 4, June 1, 2018                                     S. Chakrabarti
                                                             E. Nordmark
                                                         Arista Networks
                                                          A. Yourtchenko
                                                            July 3,
                                                       November 28, 2017

        Support for adjustable maximum router lifetimes per-link


   The neighbor discovery IPv6 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.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2   3
   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   5
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   IPv6 Neighbor Discovery relies on IP multicast with based on the
   to be that multicast makes efficient with respect to use of available bandwidth
   and to avoid avoids generating interrupts in the network nodes.  On some
   datalink layers multicast may not be natively supported.  On such links
   links, any possible reduction of multicast traffic will be highly
   beneficial.  Unfortunately, due to the fixed protocol constants
   specified in
   [RFC4861] [RFC4861], it is difficult to relax the multicast timers
   for neighbor discovery.  There are already link technology specific
   clarifications describing how to tune protocol the Neighbor Discovery Protocol
   (NDP) constants for certain system systems with the
   expectation in order to reduce excess Neighbor Discovery Protocol (NDP)
   NDP traffic. e.g.  [RFC6459][RFC7066] contain such clarifications for
   3GPP cellular links are one existing example
   [RFC6459][RFC7066]. links.

   This document specifies updates to the IPv6 Neighbor Discovery
   Protocol [RFC4861] for relaxing increasing 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

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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 which two
   successive Router Advertisement messages are sent, therefore sent.  Therefore one
   might reason about the relationship between these two values in terms
   of the a ratio K=AdvDefaultLifetime/MaxRtrAdvInterval, which expresses
   how many Router Advertisements will be guaranteed to be sent before
   the router lifetime expiry. expires.

   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

   In a network with higher packet loss probabilities 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.

4.  Updates to RFC4861

   This document updates Section 4.2 and Section 6.2.1. of [RFC4861] to
   update the following router configuration variables.

   MaxRtrAdvInterval MUST be no greater than 65535.  AdvDefaultLifetime
   MUST either be zero (the router is not

   In Section 4.2, inside the paragraph that defines Router Lifetime,
   change 9000 to be used as a default
   router) or be a value between MaxRtrAdvInterval and 65535. 65535 seconds.

   In Section 6.2.1, inside the paragraph that defines
   MaxRtrAdvInterval, change 1800 to 65535 seconds.

   In Section 6.2.1, inside the paragraph that defines
   AdvDefaultLifetime, change 9000 to 65535 seconds.

   As explained in Section 3, the relationship between MaxRtrAdvInterval
   and AdvDefaultLifetime must be chosen to take into account the
   probability of packet loss.

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
   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 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, Jeena Rachel John, Brian Carpenter, Tim Chown and Chown, Fernando
   Gont Gont,
   Warren Kumari and Adam Roach for their comments and suggestions that
   improved this document.

9.  References

9.1.  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,

   [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,

9.2.  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,

   [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,

   [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,

   [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, <http://www.rfc-editor.org/info/rfc7066>. <https://www.rfc-editor.org/info/rfc7066>.

Authors' Addresses

   Suresh Krishnan
   335 Rue Peel
   Montreal, QC

   Email: suresh@kaloom.com
   Jouni Korhonen
   Porkkalankatu 24
   FIN-00180 Helsinki

   Email: jouni.nospam@gmail.com

   Samita Chakrabarti

   Email: samita.chakrabarti@ericsson.com

   Erik Nordmark
   Arista Networks
   Santa Clara, CA

   Email: nordmark@acm.org

   Andrew Yourtchenko
   6b de Kleetlaan
   Diegem  1831

   Email: ayourtch@cisco.com