Step 1: Write down the IP address

To calculate the subnet mask from an IP address, you first need to write down the IP address. For example, let’s say the IP address is 192.168.0.1.

Step 2: Convert the IP address to binary

The next step is to convert the IP address to binary. To do this, write down the IP address in binary form. For example, the binary form of 192 is 11000000, the binary form of 168 is 10101000, the binary form of 0 is 00000000, and the binary form of 1 is 00000001.

Step 3: Determine the network bits

To determine the network bits, you need to know the class of the IP address. IP addresses are divided into classes A, B, C, D, and E. The class of the IP address is determined by the first few bits of the IP address. In our example, the IP address 192.168.0.1 is a Class C IP address, which means the first three octets are used for the network portion of the address, and the last octet is used for the host portion of the address.

Step 4: Determine the subnet mask

Now that you know the class of the IP address and the number of network bits, you can determine the subnet mask. The subnet mask is a binary number that consists of all ones for the network bits and all zeros for the host bits. For example, the subnet mask for a Class C IP address with 24 network bits would be 11111111.11111111.11111111.00000000.

Step 5: Convert the subnet mask to decimal

The last step is to convert the subnet mask from binary to decimal. In our example, the subnet mask in binary is 11111111.11111111.11111111.00000000, which is equal to 255.255.255.0 in decimal.

By following these easy steps, you can calculate the subnet mask from an IP address. Understanding subnet masks is essential for managing network devices and ensuring a smooth and secure network. Take your networking skills to the next level with our expert approach.

Follow another walkthrough of this subject here: https://www.expertnetworkconsultant.com/expert-approach-in-successfully-networking-devices/how-to-calculate-subnet-mask-from-ip-address-step-by-step/

Example 1: Subnetting a Class A Network

Let’s say we want to subnet the Class A network 10.0.0.0/8 to create smaller subnets for different departments in our organization. We want to create 4 subnets with a maximum of 2,000 hosts per subnet.

To create 4 subnets, we need to borrow 2 bits from the host portion of the IP address. This leaves us with 14 bits for the host portion of the IP address, which gives us 16,384 IP addresses (2^14) per subnet.

To determine the subnet mask for each subnet, we need to determine the value of the bits we borrowed. In this case, we borrowed the first 2 bits, which gives us a value of 192 (11000000) in binary. Therefore, the subnet mask for each subnet will be 255.255.192.0.

The table below shows the network address, subnet mask, and valid host range for each subnet:

In this example, we created 4 subnets, each with a subnet mask of 255.255.192.0. This means that each subnet has 16,384 IP addresses available for hosts.

Example 2: Subnetting a Class B Network

As previously mentioned, we have been assigned the IP address 172.16.0.0/16, which means we have 65,536 IP addresses (2^16) available for our network. However, we want to divide this network into smaller subnets.

To subnet this network, we need to borrow bits from the host portion of the IP address. Let’s say we decide to borrow 4 bits to create 16 subnets (2^4). This leaves us with 12 bits for the host portion of the IP address, which gives us 4,096 IP addresses (2^12) per subnet.

To determine the subnet mask for each subnet, we need to determine the value of the bits we borrowed. In this case, we borrowed the first 4 bits, which gives us a value of 240 (11110000) in binary. Therefore, the subnet mask for each subnet will be 255.255.240.0.

The table below shows the network address, subnet mask, and valid host range for each subnet:

In this example, we created 8 subnets, each with a subnet mask of 255.255.248.0. This means that each subnet has 8,192 IP addresses available for hosts.

Example 3: Subnetting a Class C Network

A Class C network has an IP address range of 192.0.0.0 to 223.255.255.0. Let’s say we have been assigned the IP address 192.168.0.0/24 and we want to subnet it. This means we have 256 IP addresses (2^8) available for our network. However, we want to divide this network into smaller subnets.

To subnet this network, we need to borrow bits from the host portion of the IP address. In this case, we will borrow 3 bits to create 8 subnets (2^3). This leaves us with 5 bits for the host portion of the IP address, which gives us 32 IP addresses (2^5) per subnet.

To determine the subnet mask for each subnet, we need to determine the value of the bits we borrowed. In this case, we borrowed the first 3 bits, which gives us a value of 224 (11100000) in binary. Therefore, the subnet mask for each subnet will be 255.255.255.224.

The table below shows the network address, subnet mask, and valid host range for each subnet:

Conclusion

Subnetting can seem daunting at first, but it is an important tool for managing IP addresses and optimizing network performance. By dividing a larger network into smaller subnets, we can reduce broadcast traffic and improve network security. The examples above demonstrate how subnetting works and how to determine the subnet mask and valid host range for each subnet.

If you’re new to subnetting, it’s important to take the time to understand the basics before diving into more complex examples.

For additional resources and information on subnetting;

Subnetting Practice: https://www.subnettingpractice.com/
IP Subnet Calculator: https://www.calculator.net/ip-subnet-calculator.html