Neighbor Unreachability Detection is too impatient
draft-ietf-6man-impatient-nud-04

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6MAN WG                                                      E. Nordmark
Internet-Draft                                       Cisco Systems, Inc.
Updates: 4861 (if approved)                                 I. Gashinsky
Intended status: Standards Track                                  Yahoo!
Expires: April 4, 2013                                          Oct 2012

           Neighbor Unreachability Detection is too impatient
                  draft-ietf-6man-impatient-nud-04.txt

Abstract

   IPv6 Neighbor Discovery includes Neighbor Unreachability Detection.
   That function is very useful when a host has an alternative, for
   instance multiple default routers, since it allows the host to switch
   to the alternative in short time.  This time is 3 seconds after the
   node starts probing by default.  However, if there are no
   alternatives, this is far too impatient.  This document specifies
   relaxed rules for Neighbor Discovery retransmissions that allows an
   implementation to choose different timeout behavior based on whether
   or not there are alternatives.  This document updates RFC 4861.

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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on April 4, 2013.

Copyright Notice

   Copyright (c) 2012 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

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   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  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Definition Of Terms . . . . . . . . . . . . . . . . . . . . . . 4
   3.  Protocol Updates  . . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Example Algorithm . . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8

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1.  Introduction

   IPv6 Neighbor Discovery [RFC4861] includes Neighbor Unreachability
   Detection (NUD), which detects when a neighbor is no longer
   reachable.  The timeouts specified are very short (by default three
   transmissions spaced one second apart).  That can be appropriate when
   there are alternative paths over which the packets can be sent.  For
   example, if a host has multiple default routers in its Default Router
   List, or if the host has a Neighbor Cache Entry (NCE) created by a
   Redirect message.  The effect of NUD reporting a failure in those
   cases is that the host will try the alternative; the next router in
   the Default Router List, or discard the NCE which will also send
   using a different router.

   For that reason the timeouts in [RFC4861] were chosen to be short;
   this ensures that if a default router fails the host can use the next
   router in less than 45 seconds (taking into account a default
   ReachableTime of 30 seconds and the time spent in the DELAY state).

   However, when there is no alternative there are several benefits in
   making NUD try probing for a longer time.  One of those benefits is
   to be more robust against transient failures, such as spanning tree
   reconvergence and other layer 2 issues that can take many seconds to