5. Processing of the UPA

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.

5.  Processing of the UPA

   Processing of the received UPAs is optional and SHOULD be controlled
   by the configuration at the receiver.  The receiver itself, based on
   its configuration, decides what the UPA will be used for and what
   applications, if any, will be notified when UPA is received.  Usage
   of the UPA at the receiver is outside of the scope of this document.

   As an example, UPA may be used to trigger BGP PIC Edge at the
   receiving router [BGP-PIC].

   Applications using the UPA cannot use the absence of the UPA to infer
   that the reachability of the prefix is back.  They must rely on their
   own mechanisms to verify the reachability of the remote endpoints.