Feb 8, 2009
Calculating The Number of Addresses Assigned to a Subnet
Most office and home networks use networks with 255 IP addresses or less in which the subnet mask starts with the numbers 255.255.255. This is not a pure networking text, so I'll not discuss larger networks because that can become complicated, but in cases where less than 255 IP addresses are required a few apply. There are only seven possible values for the last octet of a subnet mask. These are 0, 192, 128, 224, 240, 248 and 252. You can calculate the number of IP addresses for each of these by subtracting the value from 256. In many cases the subnet mask isn't referred to by the dotted decimal notation, but rather by the actual number of bits in the mask. So for example a mask of 255.255.255.0 may be called a /24 (slash 24) mask instead. A list of the most commonly used masks in the office or home environment is presented in Table .
So for example, if you have a subnet mask of 255.255.255.192, then you have 64 IP addresses in your subnet (256 - 192) |
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