Term of the Moment
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Definition: subnet mask tables
The following summarizes how networks, subnetworks and hosts are identified in the TCP/IP protocol. An IP address is first divided between networks and hosts. The host bits are further divided between subnets and hosts. See subnet mask and subnet.
Summary of Classes A, B & C
Class C Subnet Masks
There are very few Class A networks, but each one can contain thousands of subnets and hosts (defined in 24 bits).
CLASS B SUBNET MASKS (LARGE NETWORKS)
How 16
Bits Are ---Maximum---
Subnet Mask Divided Subnets/Hosts
255.255.192.0 2/14 2 16,382
255.255.224.0 3/13 6 8,190
255.255.240.0 4/12 14 4,094
255.255.248.0 5/11 30 2,046
255.255.252.0 6/10 62 1,022
255.255.254.0 7/9 126 510
255.255.255.0 8/8 254 254
255.255.255.128 9/7 510 126
255.255.255.192 10/6 1,022 62
255.255.255.224 11/5 2,046 30
255.255.255.240 12/4 4,094 14
255.255.255.248 13/3 8,190 6
255.255.255.252 14/2 16,382 2
CLASS C SUBNET MASKS (SMALL NETWORKS)
How 8
Bits Are ---Maximum---
Subnet Mask Divided Subnets/Hosts
255.255.255.192 2/6 2 62
255.255.224.224 3/5 6 30
255.255.240.240 4/4 14 14
255.255.248.248 5/3 30 6
255.255.252.252 6/2 62 2
The last 8 bits of the mask identify subnets and hosts. Network administrators have to determine how best to construct the network: more subnets and fewer hosts or more hosts and fewer subnets.