December 10, 2020

Everything You Need to Know About a Subnet Mask

A subnet, or sub-network, refers to a network within a network, which is assigned to make the parent network more efficient. Administrators use subnets to facilitate effective network traffic over a shorter distance without requiring the signals to pass through multiple routers to reach the destination.

A subnet mask is a 32-bit number like an IPv4 address but it masks the IP address for internal purposes and divides the IPv4 address into network address and host address. For instance, network routers employ subnet masks to route data packets to the specified destinations.

In general, a subnet mask comprises of network bits that are set to 1s and host bits that are set to 0s. In any network, there are two host addresses, which are reserved for special purposes and cannot be allocated to hosts. Here, the 0 address is allocated a network address while 255 is allocated to a broadcast address. Note that subnet masks are not defined by the data packets transmitted across the network; they only represent the destination IPv4 address that the router will match with a subnet.

By using subnets in a network, administrators can divide a big network into multiple smaller networks for the varied purposes of the company. This will also help to strengthen the security features of the network while allowing for better reorganization. All the hosts in a subnet will work by communicating with the packets transmitted by other nodes in the network. However, the network performance can be affected due to heavy traffic as well as collisions and retransmissions of packet data.

Applying a subnet mask will separate the network address from the host address in the IP address. For instance, take that an IP packet is assigned to the IP address 192.0.2.15, which is a Class C network. Here, the network is denoted by the first three components of the IPv4 address – 192.0.2 or 192.0.2.0/24. In such a case, the network router will forward the IP packet to a host that is indicated by 192.0.2 on the network.

When the IP packet reaches the destination network, the router in the network will check the routing table and do the binary calculations using the subnet mask of 255.255.255.0. The network router will then look for the device address “15” and determine the subnet to redirect the IP packet to. It will then forward the IP packet to the router or switch that corresponds to that particular subnet for delivering the IP packet to the IP address 192.0.2.15.