Implementing Subnetting- Understanding IP

Before you can implement subnetting, you need to determine your current requirements and plan on how best to implement your subnet scheme.

How to Determine Your Subnetting Requirements

Follow these guidelines to calculate the requirements of your subnet:

  1. Determine the number of required network IDs: one for each subnet and one for each wide area network (WAN) connection.
  2. Determine the number of required host IDs per subnet: one for each TCP/IP device, including, for example, computers, network printers, and router interfaces.
  3. Based on these two data points, create the following:

               One subnet mask for your entire network

               A unique subnet ID for each physical segment

               A range of host IDs for each unique subnet

How to Implement Subnetting

Subnetting is implemented by assigning a subnet address to each machine on a given physical network. For example, in Figure 4.3, each machine on subnet 1 has a subnet address of 1.

FIGURE 4.3 A sample subnet

The default network portion of an IP address can’t be altered without encroaching on another administrative domain’s address space, unless you are assigned multiple consecutive classful addresses. To maximize the efficient use of the assigned address space, machines on a particular network share the same network address. In Figure 4.3, you can see that all of the Widget Inc. machines have a network address of 130.57. That principle is constant. In subnetting, it’s the host address that’s manipulated— the network address doesn’t change. The subnet address scheme takes a part of the host address and recycles it as a subnet address. Bit positions are stolen from the host address to be used for the subnet identifier. Figure 4.4 shows how an IP address can be given a subnet address.

FIGURE 4.4 Network vs. host addresses

Class B address with a subnet address
Network address   Subnet  Host address
1000 0010. 0011 1001.0000 0001. 0011 1000

Because the Widget Inc. network is a Class B network, the first 2 bytes specify the network address and are shared by all machines on the network, regardless of their particular subnet. Here every machine’s address on the subnet must have its third byte read 0000 0001. The fourth byte, the host address, is the unique number that identifies the actual host within that subnet. Figure 4.5 illustrates how a network address and a subnet address can be used together.

FIGURE 4.5 The network address and its subnet

When implementing subnetting, you need some type of hardware installed onto the network. Most of us will just use a router. But if you do not want to purchase an expensive router, there is another way.

One way that you can implement subnetting is by using a Windows Server 2022 machine with multiple NIC adapters configured with routing enabled on the server. This type of router is called a multihomed router. This is an inexpensive way to set up a router using a Microsoft server, but it may not be the best way. Many companies specialize in routers, and these routers offer many more features and more flexibility than a multihomed router.

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