How to Find Your Subnet Mask

To allow for faster data transfer and easier management, networks are divided into subnetworks. Routers do this by assigning subnet masks, which are numbers that indicate where in the IP address to look to determine the subnetwork. Finding the subnet mask on a computer is usually a simple task. Other devices are more difficult to use. If you are asked to enter a subnet mask, you should usually use the same one as your computer.

Method 1 Windows Instructions

1. Launch Command Prompt. To open the Command Prompt window, press the Windows key and R at the same time.

If this fails, click the Start button or the Windows logo in the lower left corner of the screen. In the search bar, type “command prompt” and then double-click the icon that appears. To access the search bar, you may need to first press Search.

If there is no icon in the lower left, move your mouse to the lower right and swipe upward, or on a touch screen, swipe from the right.

2. Enter the ipconfig command. Type the words ipconfig /all exactly as they appear, with a space in between them. Hit the ↵ Enter key. Windows ipconfig is the program that keeps track of all of your network connections. This command will bring up a list with all of your network information.

3. Determine the subnet mask. This is in the “Ethernet Adapter Local Area Connection” section. Look for the line that starts with “Subnet Mask” and then cross it to find your subnet mask. The majority of subnet mask numbers, such as 255.255.255.0, begin with a string of 255s.

4. Instead, look through the Control Panel. Here’s another place to look for this information:

Navigate to Network & Internet Network and Sharing Center in the Control Panel.

On most modern Windows systems, on the left, click “Change adapter settings.” Instead, in Windows Vista, select “Manage Network Connections.”

Select “Status” from the context menu when you right-click “Local Area Connection.” In the new window that appears, click “Details.” Locate your subnet mask.

Method 2 Mac Instructions

1. On your dock, select the “System Preferences” icon. If that icon does not appear in your dock, click the Apple logo in the upper left corner of the screen and select “System Preferences.”

2. Select the “Network” option. On most versions of Mac OS X, the Network icon appears as a grey ball in the “System Preferences” window. If you can’t find it, enter Network in the search bar at the top right of the System Preferences window.

3. Choose your Internet connection from the drop-down menu on the left. Click on the name that has a green dot next to it and the word “Connected” beneath it.

4. If you’re using WiFi, select “Advanced.” This is in the lower right corner. On most other types of network connections, the Subnet Mask is already labelled on the right side of your screen.

5. In the “Advanced” window, click the TCP/IP tab. TCP/IP specifies the communication method for accessing a network on a Mac.

6. Locate your subnet mask. This should be labelled “Subnet Mask” and start with a 255.

If the only numbers you see are in the lower half of the screen, below “Configure IPv6,” you are on a local IPv6-only network that does not use subnet masks. If you are online, try selecting “Using DHCP” from the “Configure IPv4” drop-down menu, then clicking Renew DHCP Lease.

Method 3 Linux Instructions

1. Launch a command prompt. If you’re not sure how to do this, you’ll need to look up specific instructions for your Linux distribution. Before proceeding, you may want to become more acquainted with the command line.

2. Enter the ifconfig command. In the command line window, type ifconfig and press ↵ Enter.

If nothing happens other than a message stating that you need to be root (administrator), then follow these steps to gain administrator access.

3. Determine the subnet mask. This should be labelled “Subnet Mask” or “Mask.” The number will begin with the number 255.

Method 4 Setting Up a TV or Other Device

1. Use the same subnet mark that you would for a computer. When configuring a smart TV or other device, you may be asked to enter a subnet mask. This is a number unique to your local network. Follow the instructions above to find the subnet mask on your computer for the best results. The same number should also work for your device.

If your device continues to refuse to connect, keep the information open on your computer. Refer to it when making changes to the device’s settings.

If you are unable to locate the information on a computer, try entering 255.255.255.0. For home networks, this is the most commonly used subnet mask.

2. Alter the IP address. If the device still won’t connect to the internet, look at the IP address. This should be on the same screen as setting the subnet mask. Compare it to your computer’s IP address, which is visible wherever you found your computer’s subnet mask. Except for the final number or numbers after the last period, copy your computer’s IP address. Choose any higher number as long as it is 254 or less. Add at least ten numbers because nearby numbers are more likely to be used by other devices on your network.

Set your device’s IP address to 192.168.1.100, for example, if your computer’s IP address is 192.168.1.3.

If you can’t find your computer’s IP address, look for a printed label on your router or search online for your router’s brand and “IP address.” Change the last set of numbers.

If you still can’t find anything, try 192.168.1.100, 192.168.0.100, 192.168.10.100, or 192.168.2.100.

3. Configure the Gateway. This should be set to the same Gateway value as your computer, which is also the IP address of your router. This is almost always the same as the device’s IP address, but with a 1 in place of the last group of numbers.

Set the Gateway to 192.168.1.1, for example, if any device on your network has an IP address of 192.168.1.3.

Enter http:// followed by this value into any internet browser. You should be able to access information about your router if you have the correct gateway.

4. Configure the DNS. Use the same DNS settings as your computer, or the value you specified in Gateway. Alternatively, you can look up “public DNS” online to find more options.

5. Please contact the manufacturer. If your device still won’t connect with these settings, contact technical support at the device’s manufacturer.

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