Anycast Address
As already mentioned, anycast addresses are in the same address range as aggregatable global unicast addresses, and each participating interface must be configured as having an anycast address. Within the region where the interfaces containing the same anycast addresses are, each host must be advertised as a separate entry in the routing tables. If the anycast interfaces have no definable region, each anycast entry (in the worst case) has to be propagated throughout the Internet, which obviously does not scale. It is expected, therefore, that support for such global anycast addresses will be either unavailable or very restricted. Until there is more experience gained, the following restrictions are defined in RFC 2373.
An anycast address must not be used as the source address of an IPv6 packet.
An anycast address must not be assigned to an IPv6 host. It may be assigned only to an IPv6 router.
An expected use of anycast addresses is to identify a set of routers providing access to a particular routing domain. One example is the 6to4 relay anycast address that is specified in RFC 3068 and described in Chapter 10. Another possibility is to configure with a specific anycast address all the routers within a corporate network that provide access to the Internet. Whenever a packet is sent to that anycast address, it will be delivered to the closest router that provides Internet access.
A required anycast address is the subnet-router anycast address , which is defined ...
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