ZDNet Definition for: Subnet Mask Tables

Following is a list of all Class B and C subnet masks and their maximum hosts and subnets. The last two octets (16 bits) of Class B and the last octet (8 bits) of Class C addresses are divided between hosts and subnets. At the end, all Class C masks are shown in more detail.

  CLASS B SUBNET MASKS
                    How 16
                    Bits Are  Maximum   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
                    How 8
                    Bits Are   Maximum   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

Class C Subnet Masks
The last 8 bits of the mask are divided between subnets and hosts. Using a Class C address, a network administrator has to determine how best to split up the network: more subnets and fewer hosts or more hosts and fewer subnets.






Class A, B & C Subnet Masks
This is an overview of subnet masks used in all three major network classes. The IP address is first divided between networks and hosts. The host bits are further divided between subnets and hosts.

Reproduced with permission from Computer Desktop Encyclopedia. Copyright (c) 1981-2009 The Computer Language Company Inc. All rights reserved.