Handbook of IPv4 to IPv6 Transition

96  n  Handbook of IPv4 to IPv6 Transition

For any assigned anycast address, there is a longest prefix P of that address that

identifies the topological region in which all interfaces belonging to that anycast

address reside. Within the region identified by P, the anycast address must be main

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tained as a separate entry in the routing system (commonly referred to as a host

route); outside the region identified by P, the anycast address may be aggregated

into the routing entry for prefix P.

Note that, in the worst case, the prefix P of an anycast set may be the null pre

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fix; that is, the members of the set may have no topological locality. In that case,

the anycast address must be maintained as a separate routing entry throughout the

entire Internet, ...