Cannot detect devices on a different subnet
4 posts · Closed
Hi,
My router creates a guest network, and devices that connect to the guest network are on a different subnet. Devices on the primary network are 192.168.1.x, while devices on the guest network are 192.168.101.x.
I'm running WiFi Guard on a PC on the primary network. I can successfully ping devices on the guest network from cmd. I updated the Custom IP Address Range in Settings to: 192.168.1.1 - 192.168.1.255, 192.168.101.1 - 192.168.101.255.
But after I scan, I only see the devices with 192.168.1.x IP addresses; the 101.x devices don't show up (I know there are several, I can see them on my router admin page, and as I said, I can also ping them from my PC).
Why can't WiFi Guard detect the devices on 192.168.101.x?
BTW: under Settings -> Network Adapter, I see that it shows the IP address as 192.168.1.55/255.255.255.0. I wonder if the subnet specified here is somehow overriding the custom IP address range?
In your case the router does packet forwarding between 192.168.1.x and 192.168.101.x. They are different subnets, and the ARP protocol used for MAC address resolution does not work across subnets.
Since WiFi Guard uses MAC addresses for device identification, it cannot receive any MAC addresses from the guest network. This is why the devices are not listed in its output.
You can check this by typing arp -a in a command prompt and see that there are no MAC addresses for the guest network. This is because the router forwards packets back and forth instead of direct communication. So ping works, like you mentioned, but MAC address resolution does not.
In addition to the said above, as the main purpose of Guest Network is in its isolation for security reasons, it is best to disable intranet access for Guest Network in the router settings.
Hi Ann,
Thanks for your reply.
Yes, it occurred to me later last night that the whole purpose of the guest network is to prevent communication with the primary network, so of course it's not going to work. :-D
Thanks again.
Rob.