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What is Subnetting Subnetting is a way of partitioning a network at the IP level by dividing a block of addresses into a number of smaller sets. To understand what is happening, first look at some small numbers rather than a full IP address. Take the set of 'addresses' 100 to 129. If computers used decimal representation, this network of 30 addresses might naturally be split into: 100 - 109 110 - 119 120 - 129 The first two digits represent the subnet number (10,11,12), while the final digit gives the address within the subnet.

The subnetting of IP addresses can help to make better use of IP address space, for example on expansion of a network. It also allows IP addresses on networks to be divided into multiple smaller networks or subnets. The addresses for the subnets are derived from the main network address by applying a subnet mask, and as such belong to that organisation. Effective use of subnets may remove the need to obtain additional address space. Subnets also provide some advantages over one large network:

Janet is responsible for reverse delegations within the Janet IP address space, as allocated by the RIPE NCC. Therefore, Janet will undertake delegations within the following zones:

ICANN, based in the USA, controls the global allocation of IP address space. This body has allocated blocks of IP addresses to five Regional Internet Registries, one of which is RIPE NCC. Janet and other networks in Europe may apply to RIPE NCC for IP address space.