Subnet Mask

What is Subnet Mask?

• It used to differentiate the network portion and the host portions.
• It describes the class of the IP.
• It also defines the range of the IP in the network.
• By seeing we can determine the which class is the IP and whether it is sub-netted or not.

Subnet mask for different classes:

• Each class in IP address as different subnet mask.
• 0  in the subnet mask represents the host portion.
• 255 in the subnet mask represents the network portion.
• Basically 255 in the subnet mask represents the eight "1"
• Below table shows the table of subnet mask value of each class.

Importance of Subnet Mask:

• A organisation as Purchased the two range of Class C IPs for it two branches.(Total 510 IPs).
• As Organisation a 50 Hosts in each branch. (410 IPs are wasting).
• In this situation subnet mask helps by dividing the network into the sub-networks.
• Such that single range of IP can be used for the Multiple Networks.

 Subnetting:

• We will do subnetting based on number of hosts required.
• If we know the hosts we find out the total host bits and network bits to be added.
• Then we calculate the subnet mask by the no of new network bits.
• Now we divide the IPs in the particular range.
• Subnetted IP is indicated by slash followed by number.