IPv6 Multicast and Anycast Address

Multicast Address:

A multicast address is logical address for a group of hosts in a network / beyond network. So a packet destined to a multicast address will be delivered to all the interfaces identified by that address. The broadcast address in IPv4 has been eliminated by multicast address of IPv6. To perform the task of broadcast a new type of multicast address i. e. Solicited Node Multicast address has been introduced in IPv6. IPv6 multicast is routable, and routers will not forward multicast packets unless there are members of the multicast groups to forward the packets to.

The Multicast address prefix is FF00::/8 Already some multicast address is reserved for some services. 

A picture of Multicast packet flow from WIKI.

There are also some types of multicast address. I will discuss about those here.

I will discuss the Solicited Node Multicast address in my next post.

Anycast Address:

An anycast address is a single address assigned to multiple nodes. The difference with multicast is: it will not deliver packets to all the nodes with the same address. A packet destined to an anycast address will be delivered to the nearest / first available node only.

 A very useful application of anycast address is DNS. If you have a large network with several zones in several cities you can configure your DNS / other applications with Anycast address. As a result the service will be served by the nearest DNS / application server.

Here is a picture from WIKI.