Anycast Nedir

Giriş
Anycast bir IP'ye birden fazla sunucunun hizmet vermesidir.

Google DNS
Örneğin Google DNS 8.8.8.8 farklı konumlardaki sunucular tarafından anons edilir. Dünyanın farklı yerlerinden router'lar kendisine en yakın olan kümeyi (dns cluster) tablosuna ekler.
Açıklaması şöyle

A router receiving multiple advertisements for the same network will choose which advertisement to place in its routing table based on the metrics of the routing protocol. This results in the closest (from the perspective of the routing protocol metrics) destination being used by a router.

Faydası Nedir
- Sunucunun cevap verme süresi kısalır.
- Dağıtık bir yapı olduğu için bir kümenin (cluster) erişilemez olması hizmeti kesintiye uğratmaz.

AnyCast Aslında Unicast Gidibir
Açıklaması şöyle.

Anycast is unicast. It is just that the same network is in two different places, and the routing protocol chooses the closest network to which it send traffic destined for that network.

Kendi Router'ım Anycast Kümesini Nasıl Seçer
Açıklaması şöyle.

Anycast is simply that the same network is advertised from multiple places. A router receiving multiple advertisements for the same network will choose which advertisement to place in its routing table based on the metrics of the routing protocol. This results in the closest (from the perspective of the routing protocol metrics) destination being used by a router.

For example, the primary way that BGP determines which of multiple destinations is the closest by the number of ASes in the AS_PATH attribute. If a router receives five advertisements for the 8.8.0.0/16 network, it will choose one to place in its routing table, and it will route the traffic destined for 8.8.8.8 to that network. If the site with that network goes down, the entry in its routing table will be withdrawn, and the next closest destination will be placed in its routing table.

Different routers in different locations will each make their own independent determinations as to which destination is closest. Anycast is simply advertising the same network from multiple sites and letting each router determine for itself where to send traffic destined for that network.