Multiple IP address show same MAC address
2 posts · Closed
Running Network Scanner on a system that has a wired and a wireless connection. The wired connection has an IP range of 192.168.0.x and no DHCP server. The wireless connection has a range of 10.10.10.x with a DHCP server.
When connected only to wired, I return 30 to 40 devices (this is expected).
When connected only to wireless, I return 40 to 50 devices (also expected).
When connected to both networks, I return 255 devices with 200+ all listing the same MAC address.
What could be possible reasons I am seeing these results?
It's hard to say exactly, but generally it is related to how the gateway handles the ARP protocol. As you may know, the ARP protocol is used to resolve device's IP address to MAC address and it's sent to 255.255.255.255. We also use it to see if the device is online, which is commonly known as 'arping'.
- When you are connected to 192.168.0.x only, the software would request MAC address for every device in 192.168.0.x. This works as expected.
- When you are connected to 10.10.10.x only, the software would request MAC address for every device in 10.10.10.x. This also works as expected.
- However when you are connected to both, there is a chance that requests to resolve 10.10.10.x may be sent to the 192.168.0.x and vice versa. Then the router in that network responds with is own MAC address (basically saying: this address is not here, send data through me and I'll route it).
We can probably fix this issue by ensuring that each ARP request always gets sent through the correct interface. Please try the latest version and let me know if this eliminates the problem.