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Neighbor Unreachability Detection Is Too Impatient (RFC7048) Disclosure Number: IPCOM000234062D
Original Publication Date: 2014-Jan-01
Included in the Prior Art Database: 2014-Jan-09
Document File: 16 page(s) / 18K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

E. Nordmark: AUTHOR [+1]


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 timeouts 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 those cases, when NUD fails, the host will try the alternative neighbor by redoing the next-hop selection. That implies picking the next router in the Default Router List or discarding the NCE created by a Redirect message, respectively.

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Internet Engineering Task Force (IETF)                       E. Nordmark Request for Comments: 7048                               Arista Networks Updates: 4861                                               I. Gashinsky Category: Standards Track                                         Yahoo! ISSN: 2070-1721                                             January 2014

            Neighbor Unreachability Detection Is Too Impatient


   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 a short    time.  By default, this time is 3 seconds after the node starts    probing.  However, if there are no alternative neighbors, this    timeout behavior 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 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 in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,    and how to provide feedback on it may be obtained at

Nordmark & Gashinsky         Standards Track                    [Page 1]
 RFC 7048                  NUD Is Too Impatient              January 2014

 Copyright Notice

   Copyright (c) 2014 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    ( 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 Contents

   1. Introduction ...................................................