RFC 9929 - IGP Unreachable Prefix Announcement

• Status: Proposed Standard
• Published: February 2026
• Stream: IETF
• Errata: No Errata

Abstract

RFC 9929 defines Unreachable Prefix Announcement (UPA), a mechanism for IS-IS and OSPF to signal loss of reachability to an individual prefix covered by a summary. It introduces U-Flag and UP-Flag signaling for IS-IS, OSPFv2, and OSPFv3.

Contents

• 1. Introduction
• 2. Generation of the UPA
• 3. Supporting UPA in IS-IS
• 4. Supporting UPA in OSPF
• 5. Processing of the UPA
• 6. Area and Domain Partition
• 7. IANA Considerations
• 8. Security Considerations
• 9. References
• Acknowledgements
• Contributors
• Authors' Addresses

Related Resources

• Official Text: RFC 9929
• Official Page: RFC 9929 DataTracker
• Errata: RFC Editor Errata