Subnetting Basics in a Nutshell

What is a Subnet?

Networks have subnets to regulate and isolate network traffic. A Subnet creates logical groups of computing devices based on a particular configuration. The primary function of subnets is to enhance network performance in a secure environment.

How do you Identify Hosts in a Subnet?

You can identify every host in the subnet by an IP address and a logical group by a subnet mask.

A subnet mask relies on a 32-bit notation, such as 255.255.255.0. This is the familiar representation that you get to work with. Internally, a subnet mask exists in binary form, as indicated below:

11111111 11111111 11111111 00000000

Concerning the above binary notation, it is mandatory for any subnet to have all its leftmost bits to be set to ‘1’ and its rightmost bits to be ‘0’ to be valid. Either all ‘0’ bits or all ‘1’ bits indicate an invalid subnet mask.

How do we Use a Subnet Mask?

When an IP address takes a subnet mask, it splits into an extended network address and a host address. Simply put, an extended network address is a combination of the network address and the subnet number.

Subnet Basics

The standard implementation of the Internet Protocol (IP) consists of these two elements in a two-level addressing mechanism. When combined with the host address, a three-level scheme is achieved. The following example illustrates this concept.

Assume that a small business network with restricted access to sensitive data has the following network address:

192. 168.1.0. This is a Class C address.

The subnet mask for this IP address would be 255.255.255.0, and all computers are enabled with sending and receiving messages to their peers in the default mode.

Now consider the bit representation of this IP address. The first four bits would correspond to 1100.

These four bits define that the network address is placed in the Class C range. They also fix the length of the network address to 24 bits.

To subnet a network like this, on the left side, you have to replace more than 24 bits with ‘1’. That is to say, the 25-bit mask, 255.255.255.128 represents a two-subnet network.

Setting bits to the value ‘1’ makes another bit available in the subnet for the purpose of additional indexing subnets. In this way, two-bit subnet numbers can support as many as four subnets, and three-bit numbers can support up to eight subnets.

A Note About Reserved Subnets

Individual unique networks in the form of intranets are controlled by the governing bodies of the Internet Protocol. These subnets are private networks and intended for internal use.

In general, however, subnets allow hosts to be part of a closed network and be able to communicate with other subnets only through a router or some other form of the gateway device. This type of filtering enables secure access and reserves available bandwidth to participating hosts, enhancing processing speed and limiting undesirable access.

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