Neighbor Cache Entries on First-Hop Routers: Operational Considerations
draft-ietf-v6ops-nd-cache-init-05

Document Type Active Internet-Draft (v6ops WG)
Last updated 2020-09-14 (latest revision 2020-09-06)
Replaces draft-linkova-v6ops-nd-cache-init
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v6ops                                                         J. Linkova
Internet-Draft                                                    Google
Intended status: Informational                         September 6, 2020
Expires: March 10, 2021

Neighbor Cache Entries on First-Hop Routers: Operational Considerations
                   draft-ietf-v6ops-nd-cache-init-05

Abstract

   Neighbor Discovery (RFC4861) is used by IPv6 nodes to determine the
   link-layer addresses of neighboring nodes as well as to discover and
   maintain reachability information.  This document discusses how the
   neighbor discovery state machine on a first-hop router is causing
   user-visible connectivity issues when a new (not being seen on the
   network before) IPv6 address is being used.  The various approaches
   to mitigate the problem are described, with the proposed solution
   fully documented in I-D.ietf-6man-grand.

Status of This Memo

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   This Internet-Draft will expire on March 10, 2021.

Copyright Notice

   Copyright (c) 2020 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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Linkova                  Expires March 10, 2021                 [Page 1]
Internet-Draft             NC Entries Creation            September 2020

   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
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Proposed Solution . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Solution Requirements . . . . . . . . . . . . . . . . . .   5
     2.2.  Solution Overview . . . . . . . . . . . . . . . . . . . .   5
   3.  Solutions Considered but Discarded  . . . . . . . . . . . . .   6
     3.1.  Do Nothing  . . . . . . . . . . . . . . . . . . . . . . .   7
     3.2.  Change to the Registration-Based Neighbor Discovery . . .   7
     3.3.  Host Sending NS to the Router Address from Its GUA  . . .   7
     3.4.  Host Sending Router Solicitation from its GUA . . . . . .   8
     3.5.  Routers Populating Their Caches by Gleaning From Neighbor
           Discovery Packets . . . . . . . . . . . . . . . . . . . .   9
     3.6.  Initiating Hosts-to-Routers Communication . . . . . . . .   9
     3.7.  Transit Dataplane Traffic From a New Address Triggering
           Address Resolution  . . . . . . . . . . . . . . . . . . .  10
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The section 7.2.5 of [RFC4861] states: "When a valid Neighbor
   Advertisement is received (either solicited or unsolicited), the
   Neighbor Cache is searched for the target's entry.  If no entry
   exists, the advertisement SHOULD be silently discarded.  There is no
   need to create an entry if none exists, since the recipient has
   apparently not initiated any communication with the target."

   This approach is perfectly suitable for host-to-host communications,
   which are in most cases bi-directional, and it could be expected that
   if a host A has an neighbor cache entry for the host B IPv6 address,
   host B also has the corresponding entry for the host A address in its
   cache.  However when a host communicates to off-link destinations via
   its first-hop router, that logic does not apply.  The most typical
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