Prefix Length

Prefix Length

IP addresses contain both a network and host portion. The network portion is also called a prefix. This is especially true with IPv6.

The subnet mask, shown here in CIDR notation, tells us how much of the IP address is the prefix. This leaves the rest as the host address.

Starting with IPv6, the subnet mask is called the prefix length. This is because it tells us how many bits of the full address make up the prefix, or network address.