IP Address – A Step Further

Welcome to the next step of understanding IP addresses. Now that you understand the structure of IP addresses, I want to take you through the bifurcation of IP address and the significance.

IP addresses identify a network and the host/device in the network. The closest Analogy will be a Zip code/post code in the US/UK which identifies the street (network) and the house (host/device) of the addressee. Just like the picture below.

To understand this further, we need to look at something called netmask or ‘SUBNET mask’. A Net mask tells you the part of the IP address that denotes the network (street) and the part that depicts the host (house). Routers or layer 3 devices as they are called, use a combination of the IP address and subnet mask to identify and route the data packet correctly.

For a class ‘A’ IP address, the default sub net mask will be This means that the 1st Octet is the network address and from octets 2nd to 4th are Host addresses.

Similarly, Class ‘B’ has default mask of where first 2 octets denote the network address and next 2 octets are the host addresses.

Class ‘C’ has, meaning, the 2 octets denote network and last octet denotes host addresses.

What does this bifurcation mean?

Let’s look at an example:-

An IP address  with a default mask of denotes that this host/device belongs to the network and the address of the device is Here, 1stoctet is the network and the next 3 octets denotes the address of a particular hosts. Keep with the analogy of the streets and houses, you will understand better.

However, there is one more important thing this net mask tells you and that is that there is only there is only one network i.e all hosts/ devices in this setup belong to one large pool. Nice, isn’t it. Noooooo!!!! Read on..

The concept of Many networks.

For starters, you can have all your devices (users, servers,  routers) in one single network or separate them allocating different network for each set of users as per departments, servers keeping  database and application servers in different networks for instance, Routers in different networks. Now what does this achieve?

Go back to the analogy of Streets and houses. How would a city’s addressing look where it’s just one large city and no bifurcation between streets, lanes, houses, offices etc. I reckon, the town planning authorities are going to have a tough time. A better analogy to me is a phone directory without any ordering. It’s then just a large book with lots and lots of data. How do you segregate it and make your job of finding a number easier. Well, you order the data alphabetically. That’s exactly what you do in case of networks. You order the hosts/ devices as per departments/ buildings/locations. This makes administration a hell lot easier.

Bifurcating networks & hosts by the resources/ other relevant categorizations help in:-

  • Restricting privileges.
  • Helps administrators to deal with separate networks in separate ways depending on the criticality.
  • Saves IP address space.
  • Improves performance of the network by saving memory space and processing power.

We will go into the above reasons in detail as we proceed through our topics.

How do you identify if there is one network or many networks?

 Now, this is simple. If an IP address has the default net mask, then there is 1 network.

All of my career in IT security, I have never had any client on a single network. I am sure most of the IT security professionals will agree with me.

Next we will look into subnetting (creating multiple networks) and I promise you that this is going to be challenging and interesting. The article on subnetting is the applying of the above theory in practice.

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