Allocating IP Addresses

Allocating IP Addresses

Once you have obtained a network number, decided which system to use for hostname resolution, and decided whether you're going to subnet the network, you're ready to allocate IP addresses for individual systems. For most systems, this is as simple as assigning an unused IP address from the correct net or subnet. If you use the syntax of the /etc/hosts file, this will look something like this:

150.26.80.1    green.salad.com green
150.26.80.2    tossed.salad.com tossed
150.26.80.3    jello.salad.com jello

Note: Host numbers 0 and 255 are reserved, and shouldn't be used. Systems with more than one network interface may be connected to more than one subnet, and require one address for each connected interface. Each interface should be assigned an address from the subnet that the interface is connected to. For example, if fruit.salad.com acts as a gateway between the 150.26.80 net and the 150.26.42 net, it might have the following entries:

150.26.80.19   fruit.salad.com fruit
150.26.42.1    gate-fruit.salad.com gate-fruit

Even if you're planning on using NIS or BIND for hostname resolution, you will probably want to put together an /etc/hosts file. If you install this on your systems as you attach them to the network, you'll be able to communicate while you get NIS or BIND up and running.

You should also establish some policy for allocating IP addresses for new systems once the network is in place. If your organization is large, you might want to delegate this authority to separate organizational units. For example, the branch office with its own subnet should allocate IP addresses as needed from its subnet. If your organization is divided up into subdomains, you might want to assign authority over certain subnets to subdomain administrators.