The Wi-Fi MAC protocol has a pair of header bits that mean "from AP" and "to AP." In ad-hoc mode, a designated station acts as an AP, so that's nothing special. There are a couple of non-AP modes for direct link exchanges and peer-to-peer exchances that probably don't set "from AP" but I'm not sure about that. Adrian Chadd wrote: On Sat, Nov 07, 2009, Bernhard Schmidt wrote: As already said, wireless in infrastructure mode (with access points) always sends traffic between clients through the access point, so a decent AP can filter this. How does the client determine that the traffic came from the AP versus another client? Adrian -- Richard Bennett Research Fellow Information Technology and Innovation Foundation Washington, DC