Anycast Host Addressing

Anycast host addressing is a feature of IPv4 and IPv6 networks that allows you to assign the same IP address to multiple devices. When attempting to reach a device with such an address, the employed routing protocols will route to the closest device using that address. "Closest" typically means the lowest cost or metric based on the routing protocol used.

This is useful for applications that employ globally distributed systems, allowing the same address to be used on multiple continents, thus geographically distributing traffic to such systems. This reduces latency by routing to the "closest" server to the end-user.

Anycast host addressing does not use particular address ranges, nor does it require a specific configuration. You simply assign the same address to multiple devices. However, you must make sure that the routing protocols being used correctly route such traffic. Otherwise unpredictable routing may result.

Also, you could run into issues with applications that use stateful connections such as with TCP. If one packet ends up at one server, and the other at another server, you'll have an issue.

Links

https://networklessons.com/ipv6/ipv6-address-types#Anycast https://networklessons.com/multicast/multicast-anycast-rp-configuration-cisco-ios