Networking World

Understand IPv6 Addresses

In IPv4 there were three type of addresses unicast, broadcast and multicast addresses. In IPv6 we have unicast, multicast and anycast.

The broadcast addresses are not used anymore in IPv6, because they are replaced with multicast addressing.

IPv6 addresses can be categorized by type and scope:

• Unicast addresses. A packet is delivered to one interface similar to the unicast address in IPv4.

There are further four types of unicast addresses:

• Global unicast addresses, which are conventional, publicly routable address, just like conventional IPv4 publicly routable addresses.The scope is global (IPv6 Internet addresses).
• Link-local addresses The scope is the local link (nodes on the same subnet).They are similar to the private, non-routable addresses in IPv4 (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16).
• Unique local addresses are also meant for private addressing, with the addition of being unique, so that joining two subnets does not cause address collisions.The scope is the organization (private site addressing).
• Special addresses are loopback addresses, IPv4-address mapped spaces, and 6-to-4 addresses for crossing from an IPv4 network to an IPv6 network.The scope of a special address depends on the type of special address.

• Multicast addresses. A packet is delivered to multiple interfaces.

• A packet sent to a multicast address is delivered to every interface in a group.Only hosts who are members of the multicast group receive the multicast packets. IPv6 multicast is routable, and routers will not forward multicast packets unless there are members of the multicast groups to forward the packets to.

• Anycast addresses. A packet is delivered to the nearest of multiple interfaces (in terms of routing distance).

• A packet sent to an anycast address is then delivered to the first available node. This way you can provide both load-balancing and automatic failover.