NETMASKS(5)

NAME
netmasks - the database of network masks

DESCRIPTION

The file /etc/netmasks contains a table of network masks by network number which may be used to implement subnetworks according to the IP standard. (See RFC 950).

A single entry should exist for each network that is subnetted, consisting of the network number and network mask for that network separated by white space (space or horizontal tab characters).

Network numbers and masks should be specified in the conventional IP dot notation. A network number has the same form as the internet number of a host on that network, but with the host part replaced by zeroes. A network mask has zeroes to indicate the host part of the number and ones to indicate the network part. For example,

    132.85.0.0 255.255.255.0

can be used to specify that the Class B network 132.85.0.0 should have 24 bits in the network part and 8 bits in the host part. This gives 8 bits of subnet number in addition to the normal 16 bits of Class B network number. Notice that the netmask must include at least all the bits of the standard network number, as determined by the class.

On a system configured to run NIS the contents of the netmasks file on the appropriate NIS master is used to construct the netmasks.byaddr map.

FILES
/etc/netmasks
    The database file.
/var/yp/Makefile
    This file contains appropriate commands to construct the netmasks.byaddr NIS map.

SEE ALSO
ifconfig(8C)
Postel, Jon, and Mogul, Jeff, Internet Standard Subnetting Procedure, RFC 950, Network Information Center, SRI International, Menlo Park, CA. August 1985.