Can I monitor who is using my Mac OS X Internet Sharing?

"Well, if your Airport is the only wireless router you have, you can always find out who is connected to it.

To do that :

Start Airport Utility
Double-click your Airport
Start Manual Setup mode
Navigate to Airport > Summary
Choose ""Wireless Clients""

You should now see a complete list of the clients connected to your Airport.

Alternatively, you might want to run a network sniffer program such as KisMAC or iStumbler.

EDIT : Question asked is actually referring to Internet Sharing using a Mac + in-build Airport as gateway.

In that case, since your Mac is the gateway + router, you can use a network mapper utility to ""map"" out the network, thus finding out who is connected. You can try NMap, an opensource network mapping utility."

If you want to graphically display all your local network connections, you may be interested in etherape. Otherwise, I'd go with @caliban

"arp -i bridge0 -a

If you are using Internet Sharing on Mac OS X"