Prefix Unreachable Announcement
draft-wang-lsr-prefix-unreachable-annoucement-05
LSR Working Group A. Wang
Internet-Draft China Telecom
Intended status: Standards Track G. Mishra
Expires: July 3, 2021 Verizon Inc.
Z. Hu
Y. Xiao
Huawei Technologies
December 30, 2020
Prefix Unreachable Announcement
draft-wang-lsr-prefix-unreachable-annoucement-05
Abstract
This document describes a mechanism to solve an existing issue with
Longest Prefix Match (LPM), that exists where an operator domain is
divided into multiple areas or levels where summarization is
utilized. This draft addresses a fail-over issue related to a multi
areas or levels domain, where a link or node down event occurs
resulting in an LPM component prefix being omitted from the FIB
resulting in black hole sink of routing and connectivity loss. This
draft introduces a new control plane convergence signaling mechanism
using a negative prefix called Prefix Unreachable Announcement (PUA),
utilized to detect a link or node down event and signal the RIB that
the event has occurred to force immediate control plane convergence.
Status of This Memo
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This Internet-Draft will expire on July 3, 2021.
Wang, et al. Expires July 3, 2021 [Page 1]
Internet-Draft PUA December 2020
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
3. Scenario Description . . . . . . . . . . . . . . . . . . . . 3
3.1. Inter-Area Node Failure Scenario . . . . . . . . . . . . 4
3.2. Inter-Area Links Failure Scenario . . . . . . . . . . . . 4
4. PUA (Prefix Unreachable Advertisement) Procedures . . . . . . 5
5. MPLS and SRv6 LPM based BGP Next-hop Failure Application . . 5
6. Implementation Consideration . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 7
10. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
As part of an operator optimized design criteria, a critical
requirement is to limit Shortest Path First (SPF) churn which occurs
within a single OSPF area or ISIS level. This is accomplished by
sub-dividing the IGP domain into multiple areas for flood reduction
of intra area prefixes so they are contained within each discrete
area to avoid domain wide flooding.
OSPF and ISIS have a default and summary route mechanism which is
performed on the OSPF area border router or ISIS L1-L2 node. The
OSPF summary route is triggered to be advertised conditionally when
at least one component prefix exists within the non-zero area. ISIS
Level-L1-L2 node as well generate a summary prefix into the level-2
backbone area for Level 1 area prefixes that is triggered to be
advertised conditionally when at least a single component prefix
exists within the Level-1 area. ISIS L1-L2 node with attach bit set
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