Using IPv6 Anycast ensures that when we want to connect to a group of servers, we will connect to the nearest possible server in the group. This is why anycast is referred to as “one to nearest” communication. If I want to connect to my default search engine and I’m in New York, it would be inefficient to connect to a server in Kansas, Florida, etc. I want to connect to the server that’s closest to me.

FYI: This lesson continues from the Introduction to IPv6 Address Types lesson.

Unlike so many other addresses, we can’t look at the address format and instantly know what type of address it is. This is because an anycast address doesn’t have a unique format, but refers to the way a unicast address is routed. The unicast types that can be used for anycast are Unique Local (within an organization) and Global (for routing across the internet). Notice how the server in the USA and the server in England are using the same Global Unicast Address (GUA) as their Anycast address:

IPv6 Anycast
IPv6 Anycast

How Anycast Works

The same Global Unicast Address (GUA) is assigned to multiple nodes. There's no conflict between these nodes because they understand that since this address was configured as anycast, that there are other nodes within the group that have the same GUA address.

Anycast will use the routing protocol already running on the routers to send the traffic. The routing protocols will use the path with the lowest cost.

Security and Redundancy Benefits

Distributed Denial of Service (DDOS) attacks working by infecting devices all over the Internet. Then, these devices will launch a coordinated attack to a single node. The goal is to overwhelm the victim node. This is sometimes done by sending a numerous amount of pings to the victim. Then, the victim becomes overwhelmed and can’t adequately perform its intended function. Anycast can reduce the effectiveness of DDOS attacks because traffic sent to the same address is distributed to multiple nodes.Redundancy is enhanced because anycast is sent to the nearest possible server in the group. If a server goes down, it will be sent to the next possible server.

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