I've had a big problem with a terribly slow WiFi network today which I just can't seem to trap the cause of.
- IpTables router running on a PC installed with Ubuntu 12.04 and 3 network interfaces.
- One of the interfaces (eth0) hooked up to a WiFi AP shared by all end users.
- One interface (eth1) hooked up to our ISP's modem
- One interface (eth2) hooked up to our server room's switch.
Over today, I'd been experiencing a very laggy WiFi network. Usually, I would track down one of the users doing a mass transfer of files into the server room. This is easily trackable by looking at tcpdump output of any of the interfaces.
However, today, I'm not seeing any significantly high usage on the router itself. I suspect that someone is mass transferring files between 2 laptops on the same WiFi segment (which means the packets will not go through my router).
Unfortunately, I don't know how to track this down as I don't know how to do a "tcpdump" of traffic going through the WiFi channel itself. Is there any way to accomplish this?