IP addressing within a large organisation

Introduction

The previous web pages on IP addressing have described some techniques which enable the more efficient use of IP address allocation, so as to minimise the wastefulness caused by the use of class A, B, and C addressing.

A large organisation can use some of these techniques to make the administration of IP addresses an easier task.

A typical organisation

Consider an organisation that has been allocated the class B network address of

As with all class B networks, this provides for the unique identification of 65,534 computers.

The organisation can choose to divide up this allocation using the technique of subnetting into class C networks, thus obtaining 254 different network identifications, with the capability of hosting up to 254 computers on each sub-network.

So now looking at this at the binary level - the class B network address is

with the inherent bit mask of 255.255.0.0, or

Now change the bit mask to 255.255.255.0, or

so that now there are valid network addresses from 134.36.1.0, which is

up to 134.36.254.0, which is

In most cases the organisation can assign each of these network addresses to a particular department, so that each department can host up to 254 computers on its network segment.

The process of correlating departments with network addresses, can make IP address administration an easier task, as each department can have its own local IP address administrator.

However there are some departments which require more that 254 unique computer id`s, and the solution to this is to create supernets.

An example of this could be a supernet formed for the Central Administration department - this supernet could use four of the class C networks, with the addresses of ( for example )

and the corresponding binary addresses are

For these four subnets, the bit mask used is 255.255.252.0, or in binary

With this bit mask, these four network addresses all become

or in dotted decimal notation,

and there are now 1,022 unique id`s available for the computers within the Central Administration supernet.

© 2001 Ron Turner

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