What is subnetting?

Problem Statement

Hello, there. Meet Bob, CEO of Grim Technologies. Grim Technologies has had a network consisting of only a few networking devices for the last four years. His company has plans to open five more branches with even more computing devices, which could total up to thousands of devices. This means that Grim Technologies will have a larger network. In order to solve this problem, Bob will have to subnet his large network.

So, what is subnetting?

Subnetting is the process of breaking down or splitting a large network into smaller, manageable ones. Grim Technologies may have a Class A, B, or C IP address pool available to them. They will have to take the bits reserved for assigning addresses to a host and make it a Network ID so that they can have more networks.

So, looking at Bob’s situation, why do you think he needs to subnet his network?

Reasons for subnetting

• If Bob subnets, Bob’s network will have less traffic as the network gets larger. We make subnets in order to reduce traffic in the network.
• There will be better optimization of the network performance, now that the traffic is less.
• The management of the network will be simplified when subnetted into smaller chunks.
• It will make it easier for Bob to network his new branches together because it is less expensive to have several smaller LANsmaller local area network linked together to form a single network, rather than creating a single large long-spanning WANwide area network.

How will Bob’s Grim Technologies create these subnets?

How to create a subnet

Step 1

Determine the number of required network IDs. This means that you have to identify how many LANs Bob will be creating. You will also have to identify how many WAN connections will be made from connecting the Grim Technologies LANs to each other from different WANs.

Step 2

Calculate the number of host IDs that will be needed on each of the subnets. Each of the hosts and the router interfaces require an IP address.

Step 3

Using the requirements above, create the following:

• A subnet maskA 32-bit address that allows recipients of packets in a network to tell the network ID portion from the host ID portion of an IP address for the entire network.
• A subnet ID for each of the smaller subnets which are unique to them.
• Determine the range of addresses for the hosts in each subnet.

Example

Let’s say Bob has a class C address (192.168.10.0). Let’s subnet this together for Grim Technologies:

• Bob has 5 new locations, resulting in 6 LAN. Each will be connected to a central router, creating a total of 6 Network IDs.
• Grim Technologies wishes to have 30 hosts on each of the new small networks and one router interface. These all require an address.
• 6 subnets will be enough for the $2^5$ = 32 subnet mask network. So the subnet mask will be: 256-32 = 224.

The class C address will have:

• A subnet mask of 255.255.255.224
• The number of subnets will provide the binary form of 224, which is 11100000, while noting the number of 1s and 0s.
• Number of subnets equals 2 raised to the power of the number of ones. That is $2^3$ = 8 subnets blocks. Grim Technologies will only use 6 for now.
• The valid host ID range will be 2 raised to the power of the number of ones. That is: $2^5$-2 = 32-2= 30 valid host addresses.
• Therefore, each subnet will have an address range incremented by 32, where the first and the last addresses on all of the subnets are the subnet ID and the broadcast ID respectively.

Refer to the chart below:

Subnet	Subnet ID	Broadcast ID	Valid Host ID range
1	192.168.10.0	192.168.10.31	.1 till .30
2	192.168.10.32	192.168.10.63	.33 till .62
3	192.168.10.64	192.168.10.95	.65 till .94
4	192.168.10.96	192.168.10.127	.97 till .126
5	192.168.10.128	192.168.10.259	.129 till .258

The subnet mask is 255.255.255.224.

Now we have successfully broken down Bob’s Grim Technologies network and have prevented some possible future problems from befalling the organization.