The IPv6 Address Types and Prefix Length

The IPv6 Address Types

There are three basic IPv6 address types:

Unicast - A unicast address is the most common form of an IP address and is assigned to one network interface We already learn IPv4 unicast addresses.  An IPv6 unicast address uniquely identifies an interface on an IPv6-enabled device. For communication over IPv6, source IPv6 address must be a unicast address.

IPv6 unicast have five different unicast IPv6 address types: global unicast addresses, link-local addresses, site-local addresses, unique local IPv6 unicast addresses, and special addresses. These addresses will be explained in detail in later articles.

Multicast– We also learned multicast addresses and the range of multicast addresses in IPv4 addresses. The multicast addresses identify multiple network interfaces/hosts. An IPv6 multicast address is used to send a single IPv6 packet to multiple destinations.

Anycast- An IPv6 anycast address is any IPv6 unicast address that can be assigned to multiple network devices. Like a multicast address,  anycast address identifies multiple interfaces; however, while multicast packets are accepted by multiple machines, anycast packets are delivered to the nearest device having that address.

Note - Broadcast addresses are no longer exist in IPv6. However, there is an IPv6 all-nodes multicast address that essentially gives the same result.

IPv6 Prefix Length

Remember the network portion or the prefix of an IPv4 address. The dotted-decimal subnet mask or slash notation is used to identify the network. For example, an IPv4 address of 172.16.16.100 with dotted-decimal subnet mask 255.255.0.0 is equivalent to 172.16.16.0/16.

IPv6 address uses the prefix length to represent the prefix portion. The IPv6 does not use the dotted-decimal subnet mask notation. The length of the prefix is used to specify the network portion of an IPv6 address using the IPv6 address/prefix length. The range of prefix is from 0 to 128. The typical prefix length for the most network is /64. This means the network portion or prefix of the address is 64 bit long and other 64 bit will be used for host portion. The figure illustrates the prefix of IPv6 address.