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Network Identity

00000000.00000000.0000 0000.11111111 Node Address

Notice that in every "position" where a "1" is in the net mask, the number in the unique address is brought down into the network identity. Wherever a "0" appears in the net mask, the number is brought down into the node address. This process allows a single number to be used to decompose the full TCP/IP address into the required parts of the network ID and the node ID, and allows for networking messages to be transferred to the right computing device on the correct network.

The net mask also let the network administrators adjust the size of individual networks to have fewer people on a specific network or more people. The network used in the example above with a netmask of 255.255.255.0 would have 254 node addresses available. If we were to change the net mask to 255.255.255.240, the number of nodes available would drop to only 14. By doing this, we have effectively "subnetted" the first network into 16 separate little networks of 14 nodes each. How this works will be the subject of another article, but in a quick and non-technical summary, you take two the power of the number of empty bits in the net mask (the "0"s), and subtract 2. You subtract the 2 because this represents one for the upper boundary of the network, and the second represents the lower boundary of the network.

As the first netmask that was 255.255.255.0 (1111111.11111111.11111111.000 00000) has eight empty bits, we would take 2 to the power of 8 which is 256. We subtract 2 from this total to give us a total of 254 node addresses available. In the second netmask of 255.255.255.240 (11111111.11111111.11111111.11 110000), we find four empty bits, so we take 2 to the power of 4 which is 16, and subtract 2 which gives us a total of 14 node addresses available. In subnetting our network like this, we have gone from having a single network of 254 addresses to have a total of 16 networks that have 14 addresses each.
This means that an Internet Service Provider (ISP) can utilize a single range of numbers to support a number of small clients.

Though the Internet as the global network reaching its tentacles into every computer is a myth, the global backbone ties millions of small networks into a single interwoven tapestry of computing power.

Learn more about this author, Alan Fernald.
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