How to Tell if Phones and Computers on Same Subnet
Note: If available, we highly recommend consulting an IT or networking professional when dealing with advanced network configuration issues.
Determine if a phone is on the same subnet as a computer connected to the network.
- Using the phone's menu, navigate to Status > TCIP/IP parameters (may differ slightly from phone to phone—please consult manufacturer's documentation).
- Write down both the phone's IP address and subnet mask.
- Look up the network configuration for a computer on the network:
- Open a Command Prompt (click the Windows Start button, type cmd and press Enter).
- Type ipconfig and press Enter.
- Look at the subnet mask. Does it match the phone's?
- NO: You know right away the phone and computer are not on the same network. To troubleshoot issues, rearrange the devices to ensure both the phone and computer are on the network the phones are intended to reside on.
- YES: Proceed below to determine whether or not the phone and computer are on the same subnet. (As with the subnet mask, devices on mismatched subnets must be arranged so that they reside on the same subnet to allow for productive troubleshooting of service issues.)
Compare IP addresses to determine if devices are on the same subnet.
In the example above (Step 3b), we have a subnet mask of 255.255.255.0. This tells us the size of the network block:
- In each of the four sections, if the value is 255, we will substitute that with a 0.
- If there is any other number in the section, we then subtract that number from 256.
- In the example above, we would get 0.0.0.256 (256 - 0 = 256). This is a block of 256 numbers.
If the subnet were 255.255.252.0, we substitute and get 0.0.4.256. This is a block of 1024 addresses (4 x 256 = 1024).
When comparing two IP address/subnet combinations, the addresses must match for any section where the subnet value is 255. For a subnet of 255.255.255.0, we expect to see the first three sections of the IP address match (reading left to right) if they are in the same subnet.
The key is to match up the subnet and the IP address. Let’s look at three examples:
The most common subnet you will see is 255.255.255.0. So if two addresses match in the first three sections (reading left to right), and the subnet is 255.255.255.0 for both addresses, they are in the same subnet.
Knowing what subnet a device is located in can help with network troubleshooting (especially when a device is not drawing service), as well as determining an available range when setting a static IP.