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What does it mean to 'split your network?'

I recently was addressed with a question about how to design a network, and the answer was "split your network." What is that?

Dividing a network is a practice followed my many network engineers, including myself. This helps maintain optimum bandwidth availability and also works as a good security measure when planned correctly.

In some cases, where the network is small and depending on the company's needs, it might prove a better idea not to split the network. If for example your network consists of five computers, including a server, then it might be an overkill splitting it into two or more networks since the cost will outweigh the benefits.

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So you might ask "how do you actually divide a network?" The answer is really simple, well in most cases at least… Before we continue, I should note that there are two aspects of a network, the logical part, this is where we talk about IP addresses, and the physical part, which has got to do with the actual cabling and how the computers are interconnected. The proper way of dividing a network is by making sure both of the above mentioned aspects of the network are separated.

This means, that the physical cabling and logical addresses are separated.

The logical part is taken care by assigning different addressing to each network. For example, if we have one Class C network (i.e. and would like to divide it, we can either modify its default subnet mask of to one that will satisfy our needs, or choose to use a different Class C network address for the new networks that will be introduced, i.e. we can agree to assign and to the second and third new networks respectively. This is the usual approach.

For the physical division of the network, we would have to make sure that no cable from one network, is used on another. In additional, this means that no switch, hub or other interconnecting network device should be used for more than one logical network. You can interconnect the newly separated networks by using routers or by placing gateways between them.

This was last published in September 2003

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