Knowledge Base

What is a Subnet and Why is it Needed?

A subnet is the division of an IP network into smaller, more manageable pieces. This division serves various purposes, such as improving network performance, ensuring security, and using IP addresses more efficiently. Basically, it is the separation of a large network into smaller and independent subnets.

Why is a Subnet Needed?

• Improving Network Performance: In a large network, all devices are located in the same broadcast domain. This means that a broadcast message sent by one device reaches all devices on the network. This increases network traffic and reduces performance. Subnets solve this problem by reducing broadcast domains.
• Increasing Security: Subnets increase security by isolating different parts of the network. For example, a subnet containing sensitive data can be protected against unauthorized access by keeping it separate from other subnets. Restrictions can be placed on traffic between subnets using firewalls and access control lists (ACLs).
• Efficient Use of IP Addresses: Especially due to the limited number of IPv4 addresses, it is important to use IP addresses efficiently. Subnets prevent address waste by allowing IP addresses to be distributed in smaller blocks.
• Simplifying Management: Managing a large network is difficult. Subnets simplify network management by dividing the network into smaller and more manageable pieces. Each subnet can be managed by a separate administrator or subject to different security policies.

If you would like to learn more about ASN (Autonomous System Number), you can visit our What is ASN? What Does an ASN Number Do? Comprehensive Guide page.

What is a Subnet Mask and How Does it Work?

A subnet mask is a 32-bit number (for IPv4) that determines which part of an IP address represents the network address and which part represents the host address. The subnet mask is subjected to a logical AND operation with the IP address to obtain the network address. This makes it possible to determine which network a device is on and other devices on the same network.

How Does a Subnet Mask Work?

1. Structure of the Subnet Mask: The subnet mask consists of a series of consecutive 1s followed by a series of consecutive 0s. The 1s indicate the bits representing the network address, while the 0s indicate the bits representing the host address.
2. Logical AND Operation: A logical AND operation is performed between an IP address and the subnet mask. In this operation, the corresponding bits of the IP address and the subnet mask are compared. If both bits are 1, the result is 1. Otherwise, the result is 0.
3. Obtaining the Network Address: The result of the logical AND operation yields the network address. The network address is the same for all devices on the same network.

Example:

IP Address: 192.168.1.10

Subnet Mask: 255.255.255.0

In this case, since the subnet mask is 255.255.255.0, the first 24 bits (192.168.1) of the IP address represent the network address, and the last 8 bits (10) represent the host address. The network address obtained as a result of the logical AND operation is 192.168.1.0.

Important Points:

• The subnet mask determines which part of the IP address represents the network address and which part represents the host address.
• The network address is obtained by subjecting the IP address to a logical AND operation with the subnet mask.
• The network address is the same for all devices on the same network.

What is CIDR (Classless Inter-Domain Routing) and What Advantages Does it Provide?

CIDR (Classless Inter-Domain Routing) is an IP addressing method that allows for more flexible and efficient distribution of IP addresses. In traditional class-based addressing (Class A, Class B, Class C), IP addresses were distributed in blocks of specific sizes. This led to address wastage and the growth of routing tables. CIDR was developed to solve these problems.

Advantages of CIDR:

• Preventing Address Waste: CIDR prevents address waste by allowing IP addresses to be distributed in smaller, need-based blocks.
• Reducing Routing Tables: CIDR increases routing performance by allowing fewer entries to be kept in routing tables.
• Flexibility: CIDR offers network administrators more flexibility by allowing IP addresses to be distributed in blocks of any size.

CIDR Notation:

CIDR notation is used to represent an IP address and subnet mask in a single expression. For example, 192.168.1.0/24 indicates that the 192.168.1.0 network has a 24-bit subnet mask. This means that the subnet mask corresponds to 255.255.255.0.

Example:

10.0.0.0/8 -> This indicates that the 10.0.0.0 network has an 8-bit subnet mask. This means that the subnet mask corresponds to 255.0.0.0.

172.16.0.0/16 -> This indicates that the 172.16.0.0 network has a 16-bit subnet mask. This means that the subnet mask corresponds to 255.255.0.0.

For more information on this topic, you can visit our What is CIDR? IP Addressing and Subnet Mask page.

How to Do Subnetting? Step-by-Step Explanation

Subnetting is the process of dividing an IP network into smaller subnets. This process is done to improve network performance, ensure security, and use IP addresses more efficiently. The subnetting process is done by changing the subnet mask.

Step-by-Step Subnetting:

1. Determining Needs: First, it should be determined how many subnets are needed and how many devices are needed in each subnet.
2. Determining the Subnet Mask: The appropriate subnet mask is determined according to the number of subnets and the number of devices needed. The subnet mask increases the number of subnets by increasing the number of bits representing the network address.
3. Calculating Subnet Addresses: After the subnet mask is determined, the network address is calculated for each subnet. Subnet addresses are created with consecutive numbers.
4. Determining the Valid IP Address Range: The valid IP address range is determined for each subnet. The valid IP address range is the addresses between the network address and the broadcast address.
5. Assigning IP Addresses to Devices: IP addresses are assigned to devices from the valid IP address range of the relevant subnet.

Example:

Let's assume we want to divide the 192.168.1.0/24 network into two subnets.

1. Needs: 2 subnets, approximately 128 devices in each subnet.
2. Subnet Mask: /25 (255.255.255.128)
3. Subnet Addresses:
   • 192.168.1.0/25
   • 192.168.1.128/25
4. Valid IP Address Range:
   • 192.168.1.0/25 -> 192.168.1.1 - 192.168.1.126
   • 192.168.1.128/25 -> 192.168.1.129 - 192.168.1.254
5. Assigning IP Addresses to Devices: IP addresses are assigned to devices from the above ranges.

Subnetting Calculation Tools and Methods

The subnetting process can be done manually, or it can be done using subnetting calculation tools. Subnetting calculation tools automatically calculate the subnet mask, subnet addresses, and valid IP address ranges. These tools simplify the subnetting process and prevent errors.

Subnetting Calculation Methods:

• Manual Calculation: It is possible to manually calculate the subnet mask, subnet addresses, and valid IP address ranges. This method is useful for understanding the principles of subnetting.
• Subnetting Calculation Tools: There are many online and offline subnetting calculation tools available. These tools automate the subnetting process and prevent errors.

Example Subnetting Calculation Tool:

The following Python code is an example of a simple subnetting calculation tool:

def subnet_calculator(ip_address, cidr_prefix):
  """
  Calculates subnet information for the specified IP address and CIDR prefix.
  """

  import ipaddress

  try:
    network = ipaddress.ip_network(f"{ip_address}/{cidr_prefix}", strict=False)
    print(f"Network Address: {network.network_address}")
    print(f"Broadcast Address: {network.broadcast_address}")
    print(f"Subnet Mask: {network.netmask}")
    print(f"Total Number of Hosts: {network.num_addresses - 2}") # Excluding network and broadcast addresses
    print(f"Valid Host Range: {network[1]} - {network[-2]}")

  except ValueError as e:
    print(f"Error: Invalid IP address or CIDR prefix: {e}")

# Example usage:
subnet_calculator("192.168.1.0", 24)

This code uses the `ipaddress` module to calculate the network address, broadcast address, subnet mask, and valid host range for the specified IP address and CIDR prefix. Python's `ipaddress` module provides useful tools for working with IP addresses. This module simplifies subnetting calculations and prevents errors.

Real-Life Subnetting Examples and Case Studies

Subnetting is used in many different scenarios. Here are some real-life examples and case studies:

• Corporate Networks: Large companies divide their networks into subnets based on departments or functions. For example, a separate subnet can be created for the marketing department, a separate subnet for the finance department, and a separate subnet for the development department. This helps to isolate network traffic, increase security, and simplify management.
• Data Centers: Data centers divide servers and other network devices into subnets. This helps to increase security, optimize performance, and use resources more efficiently. Separate subnets can be created for different customer environments or different services.
• Home Networks: Home users can increase security and optimize performance by dividing their home networks into subnets. For example, by creating a separate subnet for guests, their access to other devices on the home network can be restricted.
• Cloud Environments: Cloud providers divide virtual machines and other cloud resources into subnets. This helps to increase security, optimize performance, and use resources more efficiently. Separate subnets can be created for different applications or environments.

Case Study: Improving a University Network with Subnetting

A university had a large and complex network. The network was spread across different areas such as student dormitories, academic buildings, and administrative offices. Network performance was poor, there were security vulnerabilities, and management was difficult. The university decided to solve these problems by dividing the network into subnets.

Solution:

1. The university divided the network into subnets based on different areas and functions. For example, a separate subnet was created for student dormitories, a separate subnet for academic buildings, and a separate subnet for administrative offices.
2. An appropriate subnet mask was determined for each subnet.
3. Restrictions were placed on traffic between subnets using firewalls and ACLs.
4. A central system was established for network management.

Results:

• Network performance increased significantly.
• Security vulnerabilities were closed.
• Network management became easier.

Subnetting and Routing Relationship

Subnetting and routing are closely related. Routing is the process of delivering data packets between networks to the correct destination. Subnetting simplifies and makes the routing process more efficient by dividing networks into smaller parts.

Routing Tables:

Routers use routing tables to decide where to send data packets. Routing tables contain destination network addresses and the IP address of the next router (next hop) to use to reach those networks. Subnetting improves routing performance by keeping fewer entries in routing tables.

CIDR and Routing:

CIDR is a method used to reduce the size of routing tables. CIDR enables more flexible and efficient distribution of IP addresses, allowing fewer entries to be kept in routing tables. For example, multiple small networks can be represented as a single CIDR block. This helps to keep fewer entries in routing tables and improve routing performance.

If you would like to learn more about BGP (Border Gateway Protocol) configuration, you can visit our BGP Configuration page. BGP is a protocol used to share routing information between different autonomous systems (AS). Subnetting and CIDR help BGP operate more efficiently.

Summary:

Subnetting simplifies and makes the routing process more efficient by dividing networks into smaller parts. CIDR is a method used to reduce the size of routing tables. Routing tables contain destination network addresses and the IP address of the next router to use to reach those networks.

Differences Between IPv4 and IPv6 Subnetting

IPv4 and IPv6 are two different versions of the internet protocol. IPv4 uses 32-bit addresses, while IPv6 uses 128-bit addresses. This difference also affects subnetting methods and approaches.

IPv4 Subnetting:

• Due to the limited number of IPv4 addresses, it is important to minimize address waste in the subnetting process.
• IPv4 subnet masks are represented by decimal numbers (e.g., 255.255.255.0).
• IPv4 subnetting may require more complex calculations.

IPv6 Subnetting:

• Due to the abundance of IPv6 addresses, address waste is not a significant concern in subnetting.
• IPv6 subnet masks are indicated by the CIDR prefix (e.g., /64).
• IPv6 subnetting is generally simpler. For example, a /64 prefix is often used for each subnet.
• IPv6 allows devices to automatically obtain an IP address through a feature called SLAAC (Stateless Address Autoconfiguration).

Summary:

The main differences between IPv4 and IPv6 subnetting are the difference in address space size and the difference in subnetting approach. Due to the limited number of IPv4 addresses, it is important to minimize address waste in subnetting. Due to the abundance of IPv6 addresses, address waste is not a significant concern in subnetting, and subnetting is generally simpler.