Acknowledgements

This section preserves the RFC text for Unreachable Prefix Announcement (UPA), including IS-IS and OSPF signaling, U-Flag and UP-Flag semantics, propagation rules, IANA assignments, and security considerations.

Acknowledgements

   The authors would like to thank Kamran Raza, Michael MacKenzie, and
   Luay Jalil for their contributions and support of the overall
   solution proposed in this document.