Macbook as Wi-Fi sniffer
There are many tools available for 802.11 sniffing such as our own AP Remote Packet capture, Wireshark, Wildpackets Airopeek, Wildpackets Omnipeek, Cace Technologies Airpcap, Airmagnet WiFi Analyzer, etc.. The following methods allows you to use your Macbook as a sniffer (network analyzer to capture 802.11 frames).
Putting the Mac client in Monitor mode:
sudo chmod 666 /dev/bpf*
/System/Library/PrivateFrameworks/Apple80211.framework/Resources/airport -z -c 11 ( where '11' is the channel number )
This will disconnect the Macbook from using its WiFi interface for data access since it will be used as a sniffer. So only use this on a Macbook that will be used for sniffing and not 802.11 association.
If Wireshark is not installed then go to www.wireshark.org/download.html and download the appropriate release according to your OS x and chipset model.
Go to Capture->Interfaces->Options in Wireshark for the wireless interface. In Link Layer Header type, pick the '802.11 plus BSD radio Information Header'.
Now hit 'Start' to capture.
If you want to use tcpdump instead then issue the following command:
sudo tcpdump -i en1 -s0 -vvv -y IEEE802_11_RADIO >> sniffertrace.pcap