Neighbor Cache Entries on First-Hop Routers: Operational Considerations
draft-ietf-v6ops-nd-cache-init-01
v6ops J. Linkova
Internet-Draft Google
Intended status: Informational December 10, 2019
Expires: June 12, 2020
Neighbor Cache Entries on First-Hop Routers: Operational Considerations
draft-ietf-v6ops-nd-cache-init-01
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.
Status of This Memo
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This Internet-Draft will expire on June 12, 2020.
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Copyright (c) 2019 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Solution Requirements . . . . . . . . . . . . . . . . . . 4
2.2. Solution Overview . . . . . . . . . . . . . . . . . . . . 5
3. Solutions Considered but Discarded . . . . . . . . . . . . . 6
3.1. Do Nothing . . . . . . . . . . . . . . . . . . . . . . . 6
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 . . . . . . 7
3.5. Routers Populating Their Caches by Gleaning From Neighbor
Discovery Packets . . . . . . . . . . . . . . . . . . . . 8
3.6. Initiating Hosts2Routers Communication . . . . . . . . . 9
3.7. Transit Dataplane Traffic From a New Address Triggering
Address Resolution . . . . . . . . . . . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
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 host2host communications
which are in most cases bi-directional and it could be expected that
if a host A has an ND cache entry for the host B IPv6 address, the
host B also has the corresponding ND 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
scenario when the problem may arise is a host joining the network,
forming a new address and using that address for accessing the
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