Anycast provides one-to-one-of-multiple communication: the same unicast IP address is configured on multiple hosts, and routing delivers each packet to one selected host. Routers choose the best route, normally reaching the host closest to the source. This can reduce latency when the hosts provide services from different locations. section 20.5 section 20.5.5
Key properties distinguish anycast from other delivery methods:
- The address looks like an ordinary unicast address and has no reserved anycast range. section 20.5.5
- Unlike normal unicast addressing, the same address is intentionally configured on multiple hosts. section 20.5.5
- Content Delivery Network services such as Cloudflare can use globally distributed anycast servers to serve users with lower latency. section 20.5.5
Cisco IPv6 configuration
Configure an IPv6 address with the anycast keyword: `R1(config-if)# ipv6 address 2001:db8:0:100::1/64 anycast`. The keyword is not required for routing behavior, but `show ipv6 interface g0/0` marks the address with `[ANY]`, clarifying the configuration’s intent. section 20.5.5 section 20.6
