Networks can be divided into subnetworks for faster data transfer and easier management. Routers can take care of this by assigning subnet masks, a number that tells you where to look in the IP address to determine what the subnet is. In most cases, you can easily figure out a computer's subnet mask. Other devices can present a greater challenge. If you are asked to enter a subnet mask, you can usually use the same as your computer's.
Method 1 of 4: Windows instructions
Step #1. Open Command Prompt
Press the Windows key and R at the same time to open the command window.
- If this doesn't work, click the Start button or Windows logo in the lower left corner of the screen. Type 'command prompt' in the search bar and double click on the icon that appears. You may need to press Search first to open the search bar.
- If there is no icon at the bottom left, move your mouse to the bottom right, and swipe up, or swipe from right to left on the screen if you have a touchscreen.
Step 2. Type ipconfig
Type the words ipconfig /all, exactly as they appear here, with a space between them. Press the ↵ Enter key. The ipconfig command is a program that keeps track of your network connections. With this command you get an overview of all your network data.
Step #3. Find the subnet mask
This can be found in the section 'Ethernet adapter LAN connection.' Find the line that starts with "Subnet mask" and look at the end to find your subnet mask. Most subnet mask numbers start with sequences of the number 255, one after the other, such as 255.255.255.0.
Step 4. If necessary, locate it via Control Panel
Here's another way to get this information:
- Navigate to Control Panel → Network & Internet → Network and Sharing Center.
- On most modern Windows systems, click "Change adapter settings" on the left. In Windows Vista, click "Manage network connections" instead.
- Right click on 'LAN connection' and select 'Status.' Click on 'Details' in the window that appears. Find your subnet mask.
Method 2 of 4: Mac Instructions
Step #1. Click on 'System Preferences' on your dock
If that icon isn't on your dock, click the Apple logo on the left side of the screen and choose "System Preferences."
Step 2. Click on 'Network'
In the System Preferences window, in most versions of Mac OS X, the Network icon looks like a gray ball. If you can't find it, type Network in the search bar at the top right of the System Preferences window.
Step 3. Select your Internet connection from the list on the left
Click on the name with a green dot next to it, and the word "Connected" below it.
Step 4. Click on 'Advanced' if you are using Wi-Fi
You will find this at the bottom right. With most other network connection types, you can see Subnet Mask as a label on the right side of the screen.
Step 5. Select the TCP/IP tab in the 'Advanced' window
Mac TCP/IP is a specification of the communication method to access the network.
Step 6. Find your subnet mask
This should be clearly marked as "Subnet Mask," and start with the number 255.
If the only numbers you see are in the bottom half of the screen, under 'Configure IPv6,' then you only have a local IPv6-only network, which does not use subnet masks. If you want to connect to the internet, select 'DHCP' from the 'IPv4' configuration menu, and press Renew DHCP lease
Method 3 of 4: Linux instructions
Step #1. Open a command prompt
If you're not sure how to do this, you'll need specific instructions for your version of Linux. In addition, try to learn more about the command line before proceeding.
Step 2. Type ifconfig
In the command window, type ifconfig and press ↵ Enter.
If nothing happens other than a prompt to log in as root (superuser), check wikiHow for instructions on how to get superuser access
Step #3. Find the subnet mask
This is referred to as "Mask" or "Subnet Mask." The number starts with the number 255.
Method 4 of 4: Set up a TV or other device
Step 1. Use the same subnet mask as your computer
When you configure a smart TV or other device, you may be asked to enter a subnet mask. This number is specific to your local network. For best results, follow the instructions above to locate the subnet mask on your computer. You can also use the same number for this device.
- If the device won't connect, leave the information open on your computer. Please refer to it while changing your device's settings.
- If you can't find the information on your computer, enter 255.255.255.0 to try it. This is the most common subnet mask for networking.
Step 2. Change the IP address
If the device still won't go online, check the IP address. This can be found in the same screen as the subnet mask. Compare this to your computer's IP address, where you found your computer's subnet mask. Copy your computer's IP address, except for the last digit or number (after the last dot). Instead, pick a higher number, as long as it's 254 or lower. Add at least 10, because numbers that are too close are likely to be used by other devices on your network.
- For example, if your computer's IP address is 192.168.1.3, set your device's to 192.168.1.100.
- If you can't find your computer's IP address, check your router for a label with the address, or search online for your router's brand and its "IP address." Change the last group of numbers.
- If you can't find any data, try 192.168.1.100, or 192.168.0.100, or 192.168.10.100, or 192.168.2.100.
Step 3. Set up the gateway
This should be the same gateway value as your computer's, which is the same as your router's IP address. This is almost identical to the IP address of the device, except that the last group of digits has been replaced by a 1.
- For example, if your network has an IP address like 192.168.1.3, set the gateway to 192.168.1.1.
- In an internet browser, type http: followed by this value. If you have a correct gateway, you should enter the information about your router.
Step 4. Set up the DNS
Use the same DNS setting as your computer's, or the same value you entered under Gateway. Alternatively, you can also search online for 'public DNS' for more options.
Step 5. Contact the manufacturer
If your device still won't connect despite these settings, please contact the device manufacturer's technical support.
- If your subnet mask is all zeros (0.0.0.0), you may not have an active internet connection.
- The subnet mask will appear on the active adapter. For example, if you use a wireless network card, the subnet mask will be under the relevant card. If you have more than one network adapter, such as a wireless and an Ethernet card, you may have to scroll up and down to find the field.
- Networks with only IPv6 do not use subnet masks. The subnet ID is built into the IP address instead. The fourth group of digits, separated by a semicolon, describes your subnet (or the 49th–64th digits).