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How to Calculate Subnet Mask From IP Address Step by Step

Understanding a subnet mask from an IP address is like peeling back the layers of an onion to reveal its core.

Subnetting is a concept you’ve probably encountered in your networking journey, and now we’ll break down the process of calculating subnet masks step by step.

Whether you’re a beginner looking for clarity or someone wanting to reinforce their knowledge, understanding subnet masks is crucial for network configurations and operations.

So, let’s unravel the complexities of subnet masks, empowering you to confidently use this vital networking tool.

Steps to Calculate the Subnet Mask from IP Address

Understanding how to calculate the subnet mask is crucial for effectively managing network addresses and optimizing network performance.

To calculate the subnet mask, follow these steps:

  1. Determine the number of subnet bits: Decide how many bits you want to allocate for the subnet. This will depend on the size and requirements of your network.
  2. Convert the binary subnet bits to decimal: in order to determine the subnet mask.
  3. Identify the network portion: The network portion of the IP address will remain unchanged. The host portion will be used to create subnets.
  4. Combine the network portion with the subnet bits: Merge the network portion of the IP address with the subnet bits to obtain the subnet mask.

1. Understand IP Address Classes

IP address classes are used to organize and allocate IP addresses within a network. They divide IP addresses into different categories based on the number of network and host bits they contain. This allows for efficient allocation of IP addresses and helps in organizing network infrastructure.

Understanding IP address classes gives you the freedom to design and manage your network according to your specific needs. By knowing the class of an IP address, you can determine the default subnet mask and the range of available IP addresses within that network.

This knowledge empowers you to make informed decisions about IP address allocation, subnetting, and network design. It allows you to tailor your network to your unique requirements, ensuring optimal performance and scalability.

2. Convert the IP Address to Binary

Converting an IP address to binary involves breaking down the numerical components of the address into their binary equivalents. For example, let’s take the IP address

To convert this to binary, start by converting each decimal number to its 8-bit binary equivalent. For 192, it’s 11000000; for 168, it’s 10101000, and for 1, it’s 00000001.

When combined, these four sets of 8 bits form the binary representation of the IP address, which is 11000000.10101000.00000001.00000001.

Understanding how to convert an IP address to binary is important for various networking tasks, such as subnetting and calculating broadcast addresses. Plus, it’s a fundamental aspect of understanding how data is transmitted across networks, allowing you to troubleshoot and optimize network performance easily.

3. Determine the Network Portion

Understanding the network portion of an IP address is crucial for subnetting and network configuration. To determine the network portion of an IP address, follow these steps:

  1. Identify the Subnet Mask: The subnet mask separates the network portion from the host portion of the IP address.
  2. Perform Bitwise AND Operation: Use the subnet mask to perform a bitwise AND operation with the IP address to determine the network portion.
  3. Understand the Network Address: The result of the bitwise AND operation will give you the network address, which is the base address for the specific subnet.
  4. Consider Subnetting Requirements: Depending on the subnetting requirements, you may need to adjust the subnet mask to create smaller subnets within the network.

4. Identify the Subnet Bits

Now you’ll begin identifying the subnet bits to determine the subnet mask for your network. This step is important for ensuring that your network operates efficiently and securely.

By understanding the subnet bits, you can derive the subnet mask that meets your network’s requirements. This will help effectively manage your network’s IP addresses and divide them into smaller subnetworks.

Subnetting allows for better organization and management of network resources, improving performance and security.

Determining Subnet Bits

To determine the subnet bits, you need to analyze the given IP address and identify its class. Once you know the class, you can determine the default subnet mask and the number of subnet bits.

For Class A addresses ( to, the default subnet mask is, which means the subnet bits are the last three octets.

If the address is Class B ( to, the default subnet mask is, so the subnet bits are the last octet.

For Class C addresses ( to, the default subnet mask is, and there are no subnet bits.

Note that subnetting isn’t applicable for Class D and E addresses, which are reserved for multicast and experimental purposes.

Subnet Mask Derivation

When determining the subnet mask, you need to consider the class of the IP address and the default subnet mask associated with each class.

  • Class A addresses have a default subnet mask of “”. That means the first octet is used for the network portion.
  • Class B addresses have a default subnet mask of, allowing the first two octets for the network.
  • Class C addresses use a default subnet mask of, with the first three octets reserved for the network.

Once you know the class and default subnet mask, you can determine the number of subnet bits based on the required number of subnets and hosts.

Identifying the subnet bits is important for creating efficient subnets that allocate IP addresses effectively while maintaining network performance.

Subnetting With CIDR Notation

Subnetting with CIDR notation simplifies the representation of subnet masks by using a prefix length, which indicates the number of network bits in the mask. Instead of expressing the subnet mask as, for example, it can be written as /24 in CIDR notation. This indicates that the first 24 bits of the address are used for network identification. This more efficient way of representing subnet masks allows for easy aggregation of IP addresses into different network prefixes.

CIDR notation offers flexibility in designing and managing networks. It allows you to easily specify the size of a network and allocate IP addresses based on the required number of hosts in each subnet. This simplifies network administration and ensures efficient utilization of IP addresses.

Subnetting Practice Examples

Here are some examples that can help you practice subnetting:

  1. Example task 1: Given an IP address and subnet mask, find the network address, broadcast address, and usable IP range for the subnet.
  2. Example Task 2: Practice subnetting a Class B IP address using variable length subnet masking (VLSM) to create multiple subnets with different numbers of hosts.
  3. Example 3: Subnet a network with specific requirements, such as a certain number of subnets and hosts per subnet, and determine the appropriate subnet mask.
  4. Example 4: Work through real-world scenarios where subnetting is essential. These can be designing a network for a company with multiple departments and varying network size needs.

Understanding Subnet Mask Notation

Subnet mask notation is a way to represent the network portion of an IP address. It’s important to understand because it’s used in subnetting and IP address calculations.

Instead of using the standard decimal format, subnet mask notation is represented in binary. This helps in identifying the network and host portions of an IP address.

Subnet Mask Format

Understanding subnet mask notation is crucial for configuring network devices and efficiently managing IP address allocation. When it comes to subnet mask format, there are a few important points to keep in mind:

  • Subnet masks are usually expressed in either dotted decimal notation (e.g., or CIDR notation (e.g., /24).
  • Dotted decimal notation represents the subnet mask as a series of four octets in decimal format.
  • CIDR notation indicates the number of network bits in the subnet mask followed by a forward slash and the total number of bits in the mask.
  • It’s essential to understand how to interpret and convert between these different formats to effectively work with subnet masks.

Binary Subnet Mask

Understanding subnet masks in binary format is crucial for configuring network devices.

In binary form, each octet of the subnet mask is represented by eight digits, either 0 or 1.

For example, the decimal subnet mask would be represented in binary as 11111111.11111111.11111111.00000000.

The binary subnet mask provides a detailed understanding of how the subnet is divided and how the network and host portions are delineated.

This knowledge is essential for creating subnetworks and efficiently managing network resources.

Applying Subnet Masks to Networks

Applying subnet masks to networks allows for the division of a network into smaller subnetworks. This can help optimize the use of IP addresses. By applying subnet masks, you can create multiple subnetworks within a single network. Hence you can organize and manage your network more easily.

To apply subnet masks to networks, follow these steps:

  1. Understand the Subnetting Requirements: Determine the number of subnetworks and hosts required for each subnetwork in order to allocate the appropriate IP addresses.
  2. Choose the Right Subnet Mask: Select a subnet mask that can accommodate the required number of subnetworks and hosts while minimizing IP address wastage.
  3. Apply the Subnet Mask to Network Devices: Configure the subnet mask on network devices such as routers, switches, and computers to implement the subnetting scheme.
  4. Verify Network Connectivity: After applying the subnet mask, ensure that the devices within each subnetwork can communicate with each other and with devices in other subnetworks.