Hierarchy in Addressing

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In this class, we will try to understand “Hierarchy in Addressing.”

We have already discussed the basic concepts of IPv4 in our previous classes.

Hierarchy in Addressing

In our day-to-day life, we have different address hierarchies.

For example, the postal address consists of a flat number, street name, area name, city name, district name, state name, and country name.

The telephone number will have the country, state, exchange, and phone number.

In the same way as home address and phone number, the IP address is also hierarchically divided.

The image shows how the IP address is divided.

The first half is the prefix and the second half is the suffix of the address.

The address prefix defines the network, and the suffix defines the node in a network.

If the bits assigned for prefix is n, the suffix bits are 32-n.

For example, let’s assume that the prefix is fixed length, and the prefix’s length is 16-bits. Then the suffix length is also 16 bits.

With 16-bits 2^16 = 65536 possibilities.

So, we have a possibility of 65536 networks and 65536 nodes in each network.

The fixed-length prefix has a disadvantage.

For example, consider a small college or university network, and a college or university will not have a 65536 node. In such cases, most of the IP addresses are wasted.

In some cases where we have more than 65536 nodes, we have to construct multiple networks.

There are different problems with fixed-length prefixes, and to overcome those, we use variable-length prefixes.