IGP Unreachable Prefix Announcement
RFC 9929, “IGP Unreachable Prefix Announcement”, is a Proposed Standard document published in February 2026 by P. Psenak, C. Filsfils, D. Voyer, S. Hegde, G. Mishra. The canonical text is published by the RFC Editor.
Abstract
Summarization is often used in multi-area or multi-domain networks to improve network efficiency and scalability. With summarization in place, there is a need to signal loss of reachability to an individual prefix covered by the summary. This enables fast convergence by steering traffic, when applicable, away from the node which owns the prefix and is no longer reachable.
This document specifies protocol mechanisms in IS-IS and OSPF, together with two new flags, to advertise such prefix reachability loss.
The term "OSPF" in this document is used to refer to both OSPFv2 and OSPFv3.
What “Proposed Standard” means
An entry-level standards-track specification: stable, peer-reviewed and a solid basis for implementation, though it may still evolve before becoming an Internet Standard.
The canonical text of RFC 9929 is hosted at rfc-editor.org. Available in HTML,TXT,PDF,XML.
- RFC 9928 DHCPv4 over DHCPv6 with Relay Agent Support
- RFC 9930 Tunnel Extensible Authentication Protocol Version 1
- RFC 9927 Fixing the C-Flag in the Extended Address Registration Option
- RFC 9931 Security Considerations for Optimistic Protocol Transitions in HTTP/1.1
- RFC 9926 Prefix Registration for IPv6 Neighbor Discovery
- RFC 9932 Mutually Authenticating TLS in the Context of Federations
- RFC 9925 Unsigned X.509 Certificates
- RFC 9924 Advanced Professional Video