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Versions: 00                                                            
Internet Engineering Task Force                                 M. Smith
Internet-Draft                                               May 4, 2021
Updates: 4861 (if approved)
Intended status: Standards Track
Expires: November 5, 2021

             More Accurately Naming IPv6 RA Router Lifetime


   IPv6 Router Advertisements (RAs) have a "Router Lifetime" field,
   which specifies how long the advertising router will act as a default
   router for the receiving hosts, unless refreshed with another
   advertisement.  The field name "Router Lifetime" is quite general,
   and could easily be misunderstood to mean the bounded lifetime of all
   of the information contained in the RA.  This memo more accurately
   renames this field "Default Router Lifetime".

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
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   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 November 5, 2021.

Copyright Notice

   Copyright (c) 2021 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
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Internet-DrafMore Accurately Naming IPv6 RA Router Lifetime     May 2021

   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.  Updates to RFC4861  . . . . . . . . . . . . . . . . . . . . .   3
   3.  Zero Value Default Router Lifetime Example Use Case . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Change Log [RFC Editor please remove] . . . . . . . . . . . .   4
   7.  Informative References  . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   According to [RFC4861], Router Advertisements (RAs) are used by IPv6
   routers to

      [...] advertise their presence together with various link and
      Internet parameters either periodically, or in response to a
      Router Solicitation message.  Router Advertisements contain
      prefixes that are used for determining whether another address
      shares the same link (on-link determination) and/or address
      configuration, a suggested hop limit value, etc.

   The Router Lifetime field of an RA indicates whether or not the
   advertising router will act as a default router for the receiving
   IPv6 hosts, and if so, for how many seconds it will perform that
   role, unless it is refreshed by a subsequent RA from the router.  The
   router is identified by its sending interface's Link-Local address

   If the RA Router Lifetime field value is zero, it means that the
   router is not or will no longer be acting as a default router.

   Router Advertisements can carry options such as the Prefix
   Information option.  These options are required to have their own
   lifetime fields if necessary [RFC4861].

   As the field name "Router Lifetime" is quite general, and is a
   permanent field in a Router Advertisement, the purpose of this field
   can be easily misunderstood.  It could easily be misinterpreted as a
   maximum lifetime value applying to all of the parameters and options
   in the RA, acting as a constraint on all other lifetime values within
   the RA and its options.  A Router Lifetime value of zero could seem

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Internet-DrafMore Accurately Naming IPv6 RA Router Lifetime     May 2021

   to indicate that the RA is entirely invalid and that all of its
   contents should or must be ignored by the receivers of the RA.

   This memo renames the Router Lifetime field to "Default Router
   Lifetime", more accurately and explicitly describing its purpose.

2.  Updates to RFC4861

   For all instances of the term "router lifetime", the term "default
   router lifetime" is to be used, independent of letter case.

   When the term "lifetime" is used in the context of an IPv6 Router
   Advertisment, implying "router lifetime", it will now imply "default
   router lifetime."

   No other updates are needed, as the Default Router List host
   conceptual data structure, and the AdvDefaultLifetime router
   interface configuration variable, already use "default" terminology.

3.  Zero Value Default Router Lifetime Example Use Case

   The use of a non-zero Default Router Lifetime is obvious; the router
   sending these RAs is willing to act as a default router for the
   receiving hosts.

   An example of a router sending a zero value Default Router Lifetime
   is as follows.

   On a link, there is a router acting as a default router for the
   attached hosts.  This router is providing forwarding to default,
   unspecified destinations, such as the IPv6 Internet.  The router's
   RAs have a non-zero value Default Router Lifetime, such as the
   [RFC4861] AdvDefaultLifetime default value of 1800 seconds (30

   Also attached to the link is another router that is sending RAs with
   a zero value Default Router Lifetime.  This router is also attached
   to another link and path to a specific destination.  Within these RAs
   is a Route Information Option (RIO) [RFC4191], specifying an IPv6
   prefix covering the IPv6 address space reachable over the other link
   and path.

   Hosts receiving these zero value Default Router Lifetime RAs, that
   understand the Route Information Option, will send packets towards
   destinations within the prefix directly to the RIO advertising
   router, benefitting from a more optimal forwarding path, and also
   removing traffic forwarding load from the link's default router.

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   The router advertising itself as a default router will need to know
   about this other router and the address space reachable beyond it, so
   that it can forward traffic towards the the other link and path, for
   hosts that do not understand the Route Information Option.

4.  Security Considerations

   Security vulnerabilties can be created if the purpose or function of
   a mechanism is misunderstood.  Renaming the IPv6 RA Router Lifetime
   field "Default Router Lifetime" will make it clearer what the purpose
   and function of this field in IPv6 RAs is.

5.  Acknowledgements

   Review and comments were provided by YOUR NAME HERE!

   This memo was prepared using the xml2rfc tool.

6.  Change Log [RFC Editor please remove]

   draft-smith-6man-accurate-ra-router-lifetime-00, initial version,

7.  Informative References

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
              November 2005, <https://www.rfc-editor.org/info/rfc4191>.

   [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,

Author's Address

   Mark Smith
   PO BOX 521

   Email: markzzzsmith@gmail.com

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