In this session of CCNA series, we will discuss IPv4 address network and host portions, as well as subnet masks. Every machine on a network running TCP must have a unique IP address, and the bytes of IP addresses are classified into two parts: the network part and the host part. The network part specifies the unique number assigned to your network, while the host part is the part of the IP address that you assign to each host, uniquely identifying machines on your network.
The subnet mask is used to differentiate between the network and host parts of an IP address in TCP. The parts of an IP address that are used as the network and host addresses are not fixed, so they cannot be determined without additional information. This information is supplied in another 32-bit number called a subnet mask.
When an IP host is configured, a subnet mask is assigned alongside an IP address. The subnet mask signifies which part of the IP address is the network and which part is the host. The subnet mask is compared to the IP address from left to right, bit by bit. The ones in the subnet mask represent the network portion, and the zeros represent the host portion.
To illustrate this, let’s take an example of an IPv4 address: 192.168.123.132. In this example, the subnet mask is /24 or 255.255.255.0. The subnet mask, represented in binary, is 24 ones and eight zeros. By lining up the IP address and the subnet mask, we can separate the network and host portion of the address. The first 24 bits, which are the number of ones in the net mask, are identified as the network address, and the last eight bits, or the number of remaining zeros in the subnet mask, are identified as the host address.
Thus, the network address in binary format is 192.168.123.0, and the host address in binary format is 00000000. If we convert the host address to decimal format, we get a host address of 132. Therefore, for this example with a /24 subnet mask, the network ID is 192.168.123.0, and the host address is 132.
In conclusion, the subnet mask is an important tool that allows you to differentiate between the network and host portions of an IP address. With this knowledge, you can easily determine the network ID and host address for a specific IP address within a /24 subnet mask.