Understanding subnets

For administrative or technical reasons, many organizations choose to divide one network into several subnets. Subnetworking enables several local networks to appear as a single Internet network to off-site hosts. It divides the addresses for a single network to accommodate the fact that the network consists of several physical networks. You should consider using subnets in the following instances:

• When you want to hide the local network topology from the outside world. Using subnets requires only a single route to external gateways.

• When you want the ability to administer IP addresses locally. For example, a company may have an engineering subnet, a product marketing subnet, and a sales subnet, each administered by a different administrator who has control of IP addresses in a given range.

• When network bandwidth is limited due to cabling constraints. Setting up subnets, each separated by a gateway host, limits local subnet packets to those that are either destined for or sent from a local host. In this way, the overall network traffic seen by each host on the subnet is reduced.

Setting up a subnet requires you to:

• determine the appropriate IP addresses for your subnets

• configure subnet hosts with the correct IP addresses and network masks

• configure gateway hosts between subnets

Subnets allow you more flexibility when assigning network addresses. For details on network address assignment and network classes, see ``Network address''.