You can't change the lladdr (ether/macaddr) while the interface is associated with an SSID. First, disassociate from any network: sudo /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -z Then change your lladdr: sudo ifconfig <intf> lladdr 00:bb:cc:dd:ee:ff Then rejoin the WLAN normally.