Knowledge Base

What is IPv4 Subnetting and Why is it Necessary?

IPv4 subnetting is the process of dividing an IPv4 network into smaller, logical subnets. This process provides several advantages, such as using IP addresses more efficiently, increasing network performance, improving security, and simplifying network management.

• IP Address Efficiency: Subnetting prevents address waste by dividing IP addresses into smaller groups. It is especially ideal for small networks that do not require a large IP block.
• Network Performance: Subnets limit broadcast traffic, preventing devices on the network from being exposed to unnecessary traffic. This improves overall network performance.
• Security: Subnets can be used to enhance network security. For example, a subnet containing sensitive data can be isolated from other subnets.
• Network Management: Subnetting simplifies network management. Separate subnets can be created for different departments or functions, which allows for better management of network resources.

For example, if a company has 250 computers, a single Class C network (254 addresses) may not be sufficient. With subnetting, multiple subnets can be created for these 250 computers, thus using IP addresses more efficiently.

What is a Subnet Mask and How Does it Work?

A subnet mask is a 32-bit number that determines which part of an IP address represents the network address and which part represents the host address. The subnet mask is used with the IP address to determine which network a device is on and which devices it can communicate with directly.

The network address is obtained from the IP address by subjecting it to a bitwise AND operation with the subnet mask. To determine the network address, the IP address and subnet mask are subjected to a bitwise AND operation. In the AND operation, if both bits are 1, the result is 1; otherwise, the result is 0.

For example, if the IP address is 192.168.1.10 and the subnet mask is 255.255.255.0, the network address is calculated as follows:

IP Address:   192.168.1.10   (11000000.10101000.00000001.00001010)
Subnet Mask: 255.255.255.0  (11111111.11111111.11111111.00000000)
------------------------------------------------------------------
Network Address:   192.168.1.0    (11000000.10101000.00000001.00000000)

In this example, the network address is 192.168.1.0. This indicates that the device with IP address 192.168.1.10 is on the 192.168.1.0 network.

Important Points:

• The subnet mask determines the size of a network and how many host addresses it can have.
• A longer subnet mask (more 1s) indicates a smaller network and fewer host addresses.
• A shorter subnet mask (fewer 1s) indicates a larger network and more host addresses.

What is CIDR (Classless Inter-Domain Routing) Notation?

CIDR (Classless Inter-Domain Routing) is a method used to assign IP addresses more flexibly. CIDR notation is represented by an IP address followed by a slash (/) and a number. This number represents the number of 1s in the subnet mask.

For example, 192.168.1.0/24 represents a network with the IP address 192.168.1.0 and a subnet mask of 255.255.255.0 (24 ones).

CIDR notation is a shorter and easier way to specify the subnet mask. It can also be used to specify the network size.

The following table shows common CIDR notations and their corresponding subnet masks:

What are the Subnet Mask Calculation Steps?

Subnet mask calculation depends on how many subnets are needed for a specific network and how many host addresses are needed in each subnet. The steps for calculating the subnet mask are as follows:

1. Determine the Network Address: First, determine the network address you want to use. For example, 192.168.1.0.
2. Determine the Number of Subnets Needed: Determine how many subnets you need. For example, if you need 4 subnets.
3. Determine the Number of Host Addresses Needed: Determine how many host addresses you need in each subnet. For example, if you need 50 host addresses in each subnet.
4. Calculate the Required Number of Bits: Calculate the number of bits required for both subnets and hosts.
   • Number of bits required for subnets: 2ⁿ >= number of subnets (n, number of bits to be borrowed)
   • Number of bits required for hosts: 2^m - 2 >= number of hosts (m, number of bits to be allocated for the host)
5. Calculate the Subnet Mask: Calculate the subnet mask according to the required number of bits.

Example:

You want to create 4 subnets using the 192.168.1.0 network and have 50 host addresses in each subnet.

1. Network Address: 192.168.1.0
2. Number of Subnets: 4
3. Number of Host Addresses: 50
4. Required Number of Bits:
   • For subnets: 2ⁿ >= 4 => n = 2 (2 bits to be borrowed)
   • For hosts: 2^m - 2 >= 50 => m = 6 (6 bits to be allocated for hosts)
5. Subnet Mask:
   • Default subnet mask (for 192.168.1.0): 255.255.255.0 (/24)
   • When 2 bits are borrowed: 24 + 2 = 26
   • New subnet mask: 255.255.255.192 (/26)

In this case, the subnet mask will be 255.255.255.192 (/26). This allows you to create 4 subnets and have 62 (2⁶ - 2) host addresses in each subnet.

How to Use a Subnetting Calculation Tool?

Subnetting calculation tools are online tools that make it easy to calculate the subnet mask, network address, broadcast address, and other related information. These tools are very useful for people who do not understand the subnetting process or do not want to perform calculations manually.

Subnetting calculation tools usually ask for the following information:

• IP Address: Enter the IP address you want to subnet.
• Subnet Mask or CIDR Notation: Enter the subnet mask or CIDR notation.

After entering this information, the tool calculates the following information:

• Network Address: Shows the network address of the subnet.
• Broadcast Address: Shows the broadcast address of the subnet.
• Available Host Address Range: Shows the range of host addresses that can be used in the subnet.
• Total Number of Host Addresses: Shows the total number of host addresses in the subnet.
• Number of Available Host Addresses: Shows the number of host addresses that can be used in the subnet (usually 2 less than the total number of host addresses, the network address and broadcast address are subtracted).

Many different subnetting calculation tools are available online. Some popular tools include:

• Subnet Calculator (solarwinds.com)
• IP Subnet Calculator (calculator.net)
• Subnet Mask Calculator (subnet-calculator.com)

By using these tools, you can perform subnetting operations more quickly and accurately.

Real-Life Subnetting Examples and Case Studies

Subnetting is widely used in various network scenarios. Here are some real-life examples and case studies:

• Corporate Network: Separate subnets can be created for different departments of a company (e.g., marketing, sales, engineering). This helps to isolate network traffic, increase security, and simplify network management. For example, the sensitive data of the engineering department can be stored in a subnet that is inaccessible to other departments.
• Data Center: In data centers, separate subnets can be created for different servers or services. This helps to increase network performance and improve security. For example, separate subnets can be created for web servers, database servers, and application servers.
• Home Network: In home networks, separate subnets can be created for smart devices (e.g., smart TV, smart home appliances) and computers. This helps to increase security and improve network performance. For example, smart devices can be kept in a subnet that is inaccessible to computers.
• School Network: In a school, separate subnets can be created for students, teachers, and administrative staff. This helps to manage network usage and ensure security. For example, the resources that students can access can be limited, and the resources that teachers can access can be broader.

Case Study:

A university's campus network was structured as a single large network. This led to declines in network performance, security vulnerabilities, and management challenges. The university decided to reconfigure its network using subnetting. Separate subnets were created for different faculties, dormitories, and administrative buildings. This significantly increased network performance, improved security, and simplified network management.

This case study demonstrates how subnetting can be beneficial in large and complex networks.

What is Variable Length Subnet Mask (VLSM)?

Variable Length Subnet Mask (VLSM) is a subnetting technique that allows different subnet masks to be used for different subnets. This helps to use IP addresses more efficiently and make network design more flexible.

VLSM is particularly useful in situations where subnets of different sizes are needed. For example, if a network has both a large subnet (e.g., 100 hosts) and a small subnet (e.g., 10 hosts), VLSM can be used to assign an appropriate subnet mask for each subnet.

When using VLSM, a subnet mask is first calculated to accommodate the number of host addresses required for the largest subnet. Then, the remaining IP addresses are used for smaller subnets. This process continues until appropriate subnet masks have been assigned for all subnets.

Example:

You want to create three subnets using the 192.168.1.0/24 network. The sizes of the subnets are as follows:

• Subnet A: 60 hosts
• Subnet B: 30 hosts
• Subnet C: 10 hosts

Using VLSM, you can assign the following subnet masks for these subnets:

• Subnet A: 192.168.1.0/26 (255.255.255.192) - 62 hosts
• Subnet B: 192.168.1.64/27 (255.255.255.224) - 30 hosts
• Subnet C: 192.168.1.96/28 (255.255.255.240) - 14 hosts

In this example, IP addresses are used more efficiently by using VLSM. Only the necessary number of IP addresses are allocated for each subnet.

Advantages of VLSM:

• Uses IP addresses more efficiently.
• Makes network design more flexible.
• Allows for subnets of different sizes.

Disadvantages of VLSM:

• More complex than subnetting.
• Network planning may take more time.

What to Consider When Subnetting?

When subnetting, it is important to pay attention to the following points:

• Determine Network Requirements: Before subnetting, carefully determine your network's requirements. How many subnets do you need? How many host addresses do you need in each subnet? The answers to these questions will help you choose the correct subnet mask.
• Calculate the Subnet Mask Correctly: Calculating the subnet mask correctly is very important for your network to function properly. An incorrect subnet mask can lead to network connection problems and other issues.
• Prevent IP Address Conflicts: When subnetting, be careful to avoid IP address conflicts. Assign a unique IP address to each device. IP address conflicts can lead to network connection problems.
• Keep Network Documentation Up-to-Date: After subnetting, keep your network documentation up-to-date. Record network addresses, subnet masks, and other relevant information. This will help troubleshoot network problems and simplify network management.
• Don't Forget Network Security: Subnetting can be used to improve network security. However, subnetting alone is not enough. You need to take other security measures to secure your network (e.g., using a firewall, using strong passwords).
• Test: After subnetting, test your network. Make sure all devices can connect correctly and that network traffic is flowing as expected.

The following table shows common mistakes made when subnetting and how to avoid them: