Computer Network | Subnetting

Maintaining a big network and providing security to such giant networks is always a hectic task.

Where the division of networks or subnetting makes things easier.

When you have to reach to a process running in a computer of a different network, there are three things to be identified.

1. Identify the network.

   Firs the main network ID then the subnet ID. As deeper the subnetting, the identification time will become even more complex.

2. Identification of Host
3. Identification of Process

Let's subnet 172.27.172.0/24¹ (Network ID) in to two (where Directed Broadcast Address(DBA) : 172.27.172.255²).

This network has 256(2^32-24) IPs.

Subnet-1 : 172.27.172.0/25¹ ( DBA-S1 : 172.27.172.127 )

Subnet-2 : 172.27.172.128/25 ( DBA-S2 : 172.27.172.255² )

The similarity of nework ID of first subnet and directed broadcast ID of second network to those of the main network is obviously indicates that network division.

The top level router will redirect the data to main network when it sees the main network id.

Then the router below that level decides to which subnet(1 or 2) of the network the data should reroute.

• Network ID is a relative term w.r.t. router.
• If the router is over the level of concern of main network the network ID point to main network.
• else it will point to subnet.

Every subnetting reduces two IPs from the network, one for network ID and other for directed broadcast ID.

When the Subnet Masks of all the Subnets are same it is called Fixed Length Subnet Masking

An interface is the connection between to networks.

A routing table at every node lists, network ID, corresponding subnet mask and interface.

If a IP is giving any ID in the list it will mask with deful mask(0.0.0.0){of defalut NID 0.0.0.0}

Over masking an IP if it gives same network ID of the corresponding entry in routing table, the interface in that entry will be using to send the data.

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