SRv6 unreachable prefix announcement

To maintain scalability and prevent overwhelming all nodes with every prefix, route summarization at Area Border Routers (ABRs) conceal local domain details. SRv6 condenses locators from remote domains and disseminates them into the core network, which can obscure local domain activities.

A provider edge router does not immediately detect the loss of reachability when a remote edge device becomes unreachable, resulting in a traffic drop until BGP sends a status update. The ABR assigns a maximum metric to prefixes from unreachable devices, ensuring they leak across domains as Unreachable Prefix Advertisements (UPAs).

To enable the UPA, include the prefix-unreachable statement at the [edit protocols isis] hierarchy level.