Neighbor Cache Entries on First-Hop Routers: Operational Considerations
draft-ietf-v6ops-nd-cache-init-03
v6ops J. Linkova
Internet-Draft Google
Intended status: Informational July 13, 2020
Expires: January 14, 2021
Neighbor Cache Entries on First-Hop Routers: Operational Considerations
draft-ietf-v6ops-nd-cache-init-03
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 January 14, 2021.
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Internet-Draft NC Entries Creation July 2020
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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 ND cache entry for the host B IPv6 address, 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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