2. OSPFv2 Anycast Property Advertisement

Cette page resume la section correspondante du RFC 9983 et conserve les points essentiels sur OSPFv2, AC-Flag, IANA et YANG.

This document introduces a flag in the "OSPFv2 Extended Prefix TLV Flags" IANA registry to advertise the anycast property.

• Value: 0x10

• Description: Anycast Flag (AC-Flag)

The only meaning of the AC-Flag is that the prefix is intended to be advertised by multiple nodes. When a prefix is configured as anycast, the AC-Flag MUST be set. Otherwise, it MUST be clear.

The AC-Flag and the N-flag MUST NOT both be set. If both are received, the advertisement MUST be considered a configuration anomaly, the N-flag MUST be ignored, and the conflict SHOULD be logged as an operational error subject to rate limiting.

The AC-Flag MUST be preserved when the OSPFv2 Extended Prefix Opaque LSA is re-advertised into other areas. If at least one router advertising the same prefix sets the AC-Flag, the prefix is considered anycast. A prefix advertised by a single node without AC-Flag is node-specific. Anycast prefixes SHOULD be consistently managed.