IPv6 address classification — unicast, multicast & anycast

There are 3 types of IPv6 addresses-

• Unicast
• Multicast
• Anycast

IPv6 unicast just like IPv4 classes A, B, and C uses a one-to-one connection between 2 individual devices. Every unique unicast corresponds to a unique receiver on the network.

In IPv4 a broadcast communication is needed when a host doesn't know the destination address. However, there is no broadcast domain/address in IPv6. Instead, IPv6 uses multicast which is a one-to-many type of communication. A packet sent from a multicast address always has a unicast source address. Hence, a multicast address cannot be a source address.

Well-known multicast addresses are reserved for predefined groups of devices like all nodes and all routers. All nodes identified with the address of this group can receive multicast messages. All routers on the network can hear multicast messages with FF02::2 as the destination.

Solicited-Node is created by pretending the multicast address prefix FF02::1:FF0000/104 to the last 24 bits of the unicast or anycast address. A host is required to join the solicited-node group for each of its configured unicast or anycast addresses. A solicited-node address is needed for link-layer address resolution with Neighbour Discovery Protocol on the link without disturbing all nodes on the network.

Anycast is a one-to-nearest associated communication. It is usually used by routers. A packet sent to an anycast address is forwarded to the nearest router. The nearest router is determined by calculating the number of hops, distance, efficiency, latency, and cost.