Neighbor Unreachability Detection is too impatient
draft-ietf-6man-impatient-nud-06

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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: October 26, 2013                                 April 24, 2013

           Neighbor Unreachability Detection is too impatient
                  draft-ietf-6man-impatient-nud-06.txt

Abstract

   IPv6 Neighbor Discovery includes Neighbor Unreachability Detection.
   That function is very useful when a host has an alternative neighbor,
   for instance when there are multiple default routers, since it allows
   the host to switch to the alternative neighbor in short time.  This
   time is 3 seconds after the node starts probing by default.  However,
   if there are no alternative neighbors, this is far too impatient.
   This document specifies relaxed rules for Neighbor Discovery
   retransmissions that allow an implementation to choose different
   timeout behavior based on whether or not there are alternative
   neighbors.  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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

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   This Internet-Draft will expire on October 26, 2013.

Copyright Notice

   Copyright (c) 2013 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

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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   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  . . . . . . . . . . . . . . . . . . . . . . . 8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     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 for NUD are very short (by default
   three transmissions spaced one second apart).  These short can be
   appropriate when there are alternative neighbors to 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.  In these cases, when NUD fails,
   the host will try the alternative neighbor; the next router in the
   Default Router List, or discard the NCE which will also send using a
   different router.

   The timeouts specified in [RFC4861] were chosen to be short in order
   to optimize for the scenarios where alternative neighbors are
   available.

   However, when there is no alternative neighbor there are several
   benefits in making NUD try probing for a longer time.  One of those
   benefits is to make NUD more robust against transient failures, such
   as spanning tree reconvergence and other layer 2 issues that can take
   many seconds to resolve.  Marking the NCE as unreachable in that case
   causes additional multicast on the network.  Assuming there are IP