The Ultimate Guide to Finding the Subnet Mask

Subnet Mask

Networks are divided into sub-networks for faster data transfer and easier management. Routers accomplish this by assigning subnet masks, a number that indicates where in the IP address to look to determine the subnet. In most cases, finding the subnet mask on a computer is a simple matter. Other devices are a little more challenging. If you’re prompted somewhere for the subnet mask, you can usually use the same one that’s on your computer.

Instructions for Mac

Click the “System Preferences” icon in the Dock.

If you don’t have the icon in your Dock, click the apple logo in the top left and select “System Preferences”.

Click on the “Network” icon.

The Network icon in System Preferences looks like a gray sphere on most versions of OS X. If you can’t find it, type “network” into the search bar in the top-right corner.

Choose 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.

Click “Advanced” if you’re using WiFi.

This can be found at the bottom right. On most other network connections, you can already see the subnet mask on the right side of the screen.

Select the TCP/IP tab in the “Advanced” window.

Mac TCP/IP specifies the communication method for accessing the network.

Find your subnet mask.

This should be very clearly labeled “Subnet Mask” and start with 255. If the only numbers you see are in the bottom half of the screen, below “Configure IPv6,” you’re on an IPv6-only local network that doesn’t use subnet masks. If you’re connected to the internet, try selecting “Use DHCP” from the “Configure IPv4” drop-down menu, then press Renew DHCP Lease.

Instructions for Windows

Open the command line.

To do this, press the Windows key and R at the same time. If that doesn’t work, click the Start button or the Windows logo in the lower-left corner of the screen. Type “cmd” into the search bar and double-click the icon that appears. You must first click Search to see the search bar. If you don’t see an icon in the bottom left, move your mouse down and then up, or swipe from the right on a touchscreen.

Enter the ipconfig command.

Type ipconfig /all exactly like this (with the space in between). Press ↵ Enter . Windows ipconfig is the program that keeps track of your network connections. This command opens a list with all network information.

Find the subnet mask.

You can find them in the “Ethernet Card Local Area Connection” section. Find the line that starts with “Subnet Mask” and look next to it to find your subnet mask. Most subnet mask numbers start with a string of 255s, e.g.

Go to the Control Panel instead.

Here’s another way to get this information: Navigate to Control Panel → Network & Internet → Network & Sharing Center. On most modern Windows systems, click “Change card settings” on the left. On Windows Vista, click Manage Network Connections instead. Right click on “Local Area Connection” and select “Status”. In the window that opens, click on “Details”. Find your subnet mask.

Instructions for Linux

Open a command line.

If you’re not sure how to do this, you’ll need to find information specific to your distribution of Linux. You may want to familiarize yourself with the command line before proceeding.

Enter the ifconfig command.

Type ifconfig into the command line and press ↵ Enter . If nothing happens other than a message saying you must be root (administrator), you must first gain administrator access.

Find the subnet mask.

This should be labeled “Mask” or “Subnet Mask”. The number starts with 255.

Set up a TV or other device

Use the same subnet mask as a computer.

When setting up a Smart TV or other devices, you may be prompted to enter a subnet mask. This number is specific to your local network. It’s best to follow the instructions above to find the subnet mask on your computer. The same number should work for your device as well. If your device still won’t connect, leave the information open on your computer. Refer to it while changing the settings on the device. If you can’t find the information on a computer, try entering This is the most common subnet mask for home networks.

Change the IP address.

If the device still doesn’t come online, check the IP address. This should be on the same screen where you can set the subnet mask. Compare it to your computer’s IP address, which you can find from where you found your computer’s subnet mask. Copy your computer’s IP address except for the last number(s) after the last period. Choose any higher number instead, but this can only go up to a maximum of 254. Enter at least 10 as nearby numbers are more likely to be used by other devices on your network. For example, if your computer’s IP address is, set your device’s IP address to If you can’t find your computer’s IP address, look for a label printed on your router, or search the Internet for your router’s manufacturer and “IP address.” Change the last group of numbers. If you can’t find any information, try or or or

Set the gateway.

This should have the same gateway value as your computer, which is also your computer’s IP address. This is almost always the same as the device’s IP address, except with a 1 instead of the last group of numbers. For example, if a device on your network has an IP address of, set the gateway to In any browser, type http:// followed by this value. Once you have the correct gateway, you should be able to get information about your router.

Set the DNS.

Use the same DNS settings as your computer or the same value you entered under Gateway. Alternatively, search the web for “public DNS” for more options.

Contact the manufacturer.

If your device still doesn’t connect with these settings, contact technical support from the company that made the device.


If your subnet mask is all zeros (, you may not have an active internet connection. The subnet mask appears on the active map. For example, if you are using your WiFi card, the subnet mask will appear under that card. If you have more than one card, such as a WiFi card and a network card, you may have to scroll up or down to find this field. IPv6-only networks do not use subnet masks. The subnet ID is built into the IP address instead. The fourth group of digits, separated by colons, describes your subnet (or the 49th to 64th binary digits).



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