What is Subnetting?

Subnetting is the process of dividing a larger network into smaller networks or subnets. It is accomplished by borrowing bits from the host portion of an IP address and using them to create subnets. The subnet mask is used to determine the network and host portions of an IP address. The subnet mask is a 32-bit number that consists of a series of ones followed by a series of zeros. The ones represent the network portion of the address, and the zeros represent the host portion of the address.

Why Subnetting is Important?

Subnetting is essential for the following reasons:

Efficient use of IP addresses: Subnetting allows you to use IP addresses more efficiently by dividing a larger network into smaller networks. This way, you can allocate IP addresses only to devices that need them, and avoid wasting IP addresses.

Better network performance: Subnetting can improve network performance by reducing network congestion and improving network efficiency.

Improved security: Subnetting can enhance network security by isolating different segments of a network and restricting access to specific devices.

Subnetting Cheat Sheet

The following subnetting cheat sheet will help you understand the basics of subnetting:

Subnet Mask: A subnet mask is a 32-bit number that determines the network and host portions of an IP address.

Network Address: The network address is the first address in a subnet and is used to identify the network.

Broadcast Address: The broadcast address is the last address in a subnet and is used to send a message to all devices on the network.

IP Address Range: The IP address range is the set of IP addresses available for use in a subnet.

CIDR Notation: CIDR notation is a shorthand notation for representing subnet masks. It is written as a slash (/) followed by the number of bits in the subnet mask.

Subnetting Formula: The subnetting formula is used to calculate the number of subnets and hosts per subnet. The formula is 2^n, where n is the number of bits borrowed for the subnet.

Subnetting Example: To subnet a network, follow these steps:

a. Choose the number of subnets required.
b. Choose the number of host bits required per subnet.
c. Calculate the subnet mask.
d. Calculate the network address and broadcast address.
e. Determine the IP address range.

Subnet Mask	CIDR Notation	Binary Value	Decimal Value
255.255.255.0	/24	11111111.11111111.11111111.00000000	255.255.255.0
255.255.255.128	/25	11111111.11111111.11111111.10000000	255.255.255.128
255.255.255.192	/26	11111111.11111111.11111111.11000000	255.255.255.192
255.255.255.224	/27	11111111.11111111.11111111.11100000	255.255.255.224
255.255.255.240	/28	11111111.11111111.11111111.11110000	255.255.255.240
255.255.255.248	/29	11111111.11111111.11111111.11111000	255.255.255.248
255.255.255.252	/30	11111111.11111111.11111111.11111100	255.255.255.252

Conclusion:

Subnetting is an essential concept in computer networking. It allows you to divide a larger network into smaller networks, use IP addresses more efficiently, improve network performance, and enhance network security. The subnetting cheat sheet provided in this article will help you understand the basics of subnetting and become a subnetting pro. Remember to use the subnetting formula and follow the subnetting example to subnet a network successfully.

In this article, we will provide a step-by-step guide to help you understand IP subnetting.

Step 1: Determine the IP Address Class

The first step in subnetting is to determine the IP address class. IP addresses are divided into 5 classes: A, B, C, D, and E. Classes A, B, and C are commonly used for networking.

Class A networks have a default subnet mask of 255.0.0.0, Class B networks have a default subnet mask of 255.255.0.0, and Class C networks have a default subnet mask of 255.255.255.0.

Step 2: Determine the Number of Subnets Needed

The next step is to determine the number of subnets needed. This is based on the number of departments, locations, or other factors that require separate networks. To determine the number of subnets, you need to borrow bits from the host portion of the IP address.

For example, if you need 4 subnets, you need to borrow 2 bits (2^2 = 4) from the host portion of the IP address.

Step 3: Determine the Number of Hosts Needed per Subnet

The next step is to determine the number of hosts needed per subnet. This is based on the number of devices that need to be connected to the network in each subnet.

To determine the number of hosts per subnet, you need to subtract 2 from the total number of IP addresses in the subnet. The first IP address is used for the network address, and the last IP address is used for the broadcast address.

For example, if you need 100 hosts per subnet, you need to have a subnet that provides at least 102 IP addresses (100 + 2).

Step 4: Create the Subnet Mask

The subnet mask determines the range of IP addresses available for hosts in each subnet. To create the subnet mask, you need to determine the value of the bits you borrowed from the host portion of the IP address.

For example, if you borrowed 2 bits from the host portion of the IP address, you need to determine the binary value of those bits. In this case, the binary value would be 11 (2 bits).

The subnet mask for this example would be 255.255.255.192 (or /26 in CIDR notation). This subnet mask provides 64 IP addresses (2^6 = 64) per subnet.

Step 5: Determine the Valid Host Range

The valid host range is the range of IP addresses available for hosts in each subnet. To determine the valid host range, you need to subtract 2 from the total number of IP addresses in the subnet.

For example, if you have a subnet with a subnet mask of 255.255.255.192, the total number of IP addresses in the subnet is 64. Subtracting 2 gives you 62, which is the number of valid IP addresses in the subnet.

The first IP address in the subnet is used for the network address, and the last IP address is used for the broadcast address. Therefore, the valid host range for this example would be 192.168.1.1 – 192.168.1.62.

Conclusion

Subnetting is an important tool that allows you to optimize your network performance and improve security. By dividing a larger network into smaller subnets, you can reduce network congestion, increase efficiency, and create separate segments for different departments or functions within your organization.

Follow another step by step walkthrough here – https://www.expertnetworkconsultant.com/subnetting/step-by-step-guide-to-understanding-ip-subnetting/