Subnet prefix length

In IPv6, subnetting is done using the prefix length. Subnet addressing is an extension of the IP address scheme that lets a site use a single network ID for multiple physical networks. Routing outside of the site continues by dividing the IP address into a network ID and a host ID via the prefix length. Inside a site, the subnet prefix length is used to divide the IP address into a custom network ID portion and host ID portion.

For example, consider Network 2 with a /48 prefix, and add another physical network. Selecting the following subnet prefix length /50 allows for multiple physical networks:

Two bits have been used to extend the network ID. Each unique combination of bits in the part of the address specifies a different physical network. The new configuration is:

A second network with Hosts D and E has been added. Gateway G2 connects Network 2.1 with Network 2.2. Hosts D and E will use Gateway G2 to communicate with hosts not on Network 2.2. Hosts B and C will use Gateway G to communicate with hosts not on Network 2.1. When B is communicating with D, G (the configured Gateway for B) will route the data from B to D through G2.