Defining Computers, Subnetworks, and Networks

Computer, Subnetwork, and Network Tables

In the UNIX environment, networks, subnetworks, and computers (hosts) are defined in one or more of the following four network management tables:

hosts -- Names, IP addresses, descriptions, and aliases for individual computers, routers, gateways, printers, scanners, or any similar host devices
ethers -- Names and Ethernet addresses of individual computers, routers, gateways, printers, scanners, or any similar host devices
networks -- Names, IP addresses, descriptions, and aliases for networks or subnetworks
netmasks -- Netmask values that restrict valid IP addresses for computers on a given subnetwork. If you plan on creating subnetworks within a given network, then the network must have an entry in the netmasks table.
When defining netmask values, the number 255 means that the given segment of the IP addresses for computers on that subnetwork must exactly match the number used on the network for that same segment. The number 0 means that the segment can be any number from 0 to 255.
For example, a netmask of 255.255.0.0 means that IP addresses on the subnetwork must match the first two IP segments exactly, but can use any number in the last two segments. Any computer's IP address that does not match the netmask must use a gateway computer to connect to the network.
To continue with this example, in a network with an IP address of 130.155 and a netmask of 255.255.0.0, the IP addresses for all computers on that network must begin with 130.155, but can use any number from 0 to 255 for the last two segments of the IP address.