I am trying to implement a wireless hotspot solution at school where the clients are assigned a username and password that are entered in a redirect login web page. The gateway is a notebook with a NIC connected to the outside world and a wireless pcmcia card towards the local network. There is also a stand alone WAP that forwards all internal traffic. The problem is that I would like to have the users automatically logged out after a certain time of inactivity (apx 15 minutes). The approaches I have considered are:

• parsing of iptables log file
• examining timed out cached arp table entries
• dhcp lease time (not sure if applicable)

However, to have to parse all incoming/outgoing packets would put a huge strain on the gateway and to my knowledge the arp table approach is a no-no due to the built-in uncertainty in the implementation of linux arp.

If anybody has any ideas how to go on from here I would be glad to hear from you.