What Is A Subnet Mask?

How does your computer find its way around the Internet? It’s thanks in part to something called a subnet mask.

But what is a subnet mask? And why should you care? Learn how this important networking configuration parameter helps keep you connected and safe online.

What Is The Purpose Of A Subnet Mask?

A subnet mask is a 32-bit number that you use to divide an IP address into two parts:

• Network Address: This part identifies the network to which a device belongs.
• Host Address: This part identifies the specific device within that network.  

Here’s how it works:

• Binary Representation: Subnet masks are usually represented in dotted decimal notation (e.g., 255.255.255.0), but they are binary numbers that consist of 1s and 0s.
• Network Bits and Host Bits: The 1s in the subnet mask represent the network bits, and the 0s represent the host bits.  
• Network and Host Addresses: By applying the subnet mask to an IP address, you can determine the network address and the host address.  

Here’s an example:

• IP Address: 192.168.1.100
• Subnet Mask: 255.255.255.0 (in binary: 11111111.11111111.11111111.00000000)  

In this example, the first 24 bits of the IP address (192.168.1.0) represent the network address, and the last 8 bits (100) represent the hosts address range.

You use a subnet mask to:

• Divide networks into smaller subnets: Subnet masks divide large networks into smaller, more manageable segments called subnets. This helps organize devices and improve network efficiency.
• Determine network and host addresses: Subnet masks help devices identify which part of an IP address represents the network and which part represents the host. This allows devices to communicate within the same subnet or route traffic to other subnets.
• Prevent broadcast storms: Subnet masks limit the scope of broadcast traffic to a specific subnet. This prevents broadcasts from flooding the entire network, which can cause performance issues.

What Is The Difference Between A Subnet Mask & An IP Address?

While both subnet masks and IP addresses are key components of network communication, they serve distinct purposes and have different formats:

• Purpose: Your IP address identifies your device on a network, while a subnet mask helps divide a network into smaller subnets and determine which subnet your device belongs to.
• Format: IP addresses are primarily represented in dotted decimal notation, while subnet masks can be represented in binary or dotted decimal.
• Information Contained: IP addresses contain information about the network and host, while subnet masks indicate the boundary between the network and host portions of an IP address.

Your IP address can change depending on your network. For example, your home IP address differs from your work IP address. Subnet masks are usually set by your network Administrator.

Knowing the difference between an IP address and a subnet mask helps you understand how devices communicate and how networks are organized. 

How Do I Find My Computer’s IP Address & Subnet Mask?

You can find your computer’s IP address and subnet mask using built-in tools on your operating system. Here’s how:

macOS

1. Click the Apple menu and select “System Settings.”  
2. Click on the “Network” icon.  
3. Choose your active network connection (e.g., Wi-Fi or Ethernet).
4. Click on the “Details” button on your WiFi or Ethernet tab.  
5. Your IP address and subnet mask will be listed in the “TCP/IP” tab. 

Windows

1. Press the Windows key, type “cmd,” and press Enter.  
2. Run ipconfig /all command in the Command Prompt window and press Enter.  
3. Your IP address will be listed under “IPv4 Address,” and your subnet mask will be listed under “Subnet Mask.”

Linux

1. Press Ctrl+Alt+T to open a terminal window.
2. Run ifconfig command and press Enter.
3. Your IP address and subnet mask will be listed under the appropriate network interface (e.g., “eth0” or “wlan0”).

These methods should work on most modern operating systems. If you have trouble, consult your operating system’s documentation or online resources for additional help.

What Are The IP Address Classes & Their Subnet Masks?

IP addresses are categorized into three main classes: A, B, and C. Each class is designed to handle networks of different scales and comes with a default subnet mask.

1. Class A

• Range: Starts with 0 to 127 (first number in the IP address)  
• Default Subnet Mask: 255.0.0.0 
• Example: 10.0.0.1

2. Class B

• Range: Starts with 128 to 191
• Default Subnet Mask: 255.255.0.0 
• Example: 172.16.0.1

3. Class C

• Range: Starts with 192 to 223
• Default Subnet Mask: 255.255.255.0 
• Example: 192.168.0.1

While classful IP addressing was once the standard, it’s mostly replaced by Classless Inter-Domain Routing (CIDR) today, which is a more efficient way of allocating IP addresses.

What Is The Advantage of Subnetting?

Networks can be further divided using a technique called subnetting, which allows for more flexibility.

Here’s why subnetting is beneficial:

• Subnet masks help direct network traffic so that devices within the same subnet can communicate directly with each other without clogging up the entire network.
• Subnet masks help implement access control lists (ACLs) to keep unauthorized devices from accessing your network. They create boundaries, where only devices belonging to a specific subnet can communicate within it.
• Subnet masks make it easier to manage and troubleshoot your network. By dividing it into smaller groups, you can quickly identify and isolate any issues that may surface.

While subnet masks can contribute to a well-organized and secure environment for your network, you also need a multi-layered security approach to keep your data and networks safe.

What Does The Subnet Mask 255.255.255.0 Mean?

The subnet mask 255.255.255.0 is like a map for your network. Each number represents a section of your IP address that defines the network part and the device part. In this case, the first three numbers (255) mean all devices in that network share the same address, while the last number (0) means the rest of the address is unique to each device.

What Is An Example Of A Subnet?

A subnet is like a smaller group within a larger network. Each subnet has its range of IP addresses and can communicate with other subnets on the same network. For example, 172.16.1.0/24 is a subnet within the larger 172.16.0.0/16 Class B network. It’s called a subnet because it’s a subdivision of a broader network.

How To Find Default Subnet Mask From IP Address?

You can determine the default subnet mask by looking at the first octet (the first set of numbers) of your IP address. If it starts with:

• 0-127, it’s Class A, and the subnet mask is 255.0.0.0.
• 128-191, it’s Class B, and the subnet mask is 255.255.0.0.
• 192-223, it’s Class C, and the subnet mask is 255.255.255.0.

How Do Subnet Masks Improve Cybersecurity?

Subnet masks indirectly contribute to your online safety by creating barriers within your network. This limits access to sensitive data, making it harder for hackers to reach everything at once. 2Secure can help you set up and manage strong subnet masks, which adds an extra layer of protection to your network.