A way to see all connected devices?

[Jorabi]

I plugged an unknown device (it's default ip is NOT on the same subnet as all the other devices) into the back of an RT-AC87R. Activity lights come on the router and the device. I was hoping to see it appear as a mac address at least, but nothing changes in the client list. I tried the same test with another device (a camera), it didn't appear either.

Does anyone know a way to see ALL wired Ethernet devices plugged into the router regardless of what they are, or a 3rd party tool to find all connected mac addresses? I looked at nmap but it is way too complicated.

 

[ColinTaylor]

Probably the most reliable way would be to SSH into the router and issue an arp -an command.

 

[drabisan]

If unknown device doesn't have an ip address from the same subnet (like static ip, out of the subnet), arp -na will not help.
You want to learn the mac address of that device? I'm not aware of any ways to query the mac address of the physical ports. There may be one, but it may be platform dependent.

 

[Jorabi]

Thanks, I didn't know the router had SSH. I did the arp -an command and got a list of all connections, but none of the unknown devices showed up (I know all of their mac addresses). Strange. If you're wondering why I'm doing this, I cannot reach the first unknown device and I'm trying to determine if it's beyond help. It's a Ubiquiti access point. All the lights work correctly but I can't reach it using all known methods.

 

[ColinTaylor]

If unknown device doesn't have an ip address from the same subnet (like static ip, out of the subnet), arp -na will not help.

I tested this before posting, it does work. Of course this does assume that the client is trying to send out some traffic. If it's completely inert arp won't help.