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The subnet mask is used to determine the network bits and the host bits in an IP address.
A bit mask that separates the portions of an IP address significant to the network from the bits significant to the subnet. For a class C address, a standard subnet mask is 255.255.255.0, which masks the first three bytes of the address, and leaves the last byte available to identify machines on the subnet.
The method used for splitting IP networks into a series of subgroups or subnets. The mask is a binary pattern that is matched up with the IP address to turn part of the host ID address field into a field for subnets.
This feature partitions the network into segments. It is the way a router knows if a packet sent stays on the local network or needs to be passed to a different network.
