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Hello, I' ve been trying to capture packets using IEEE802_11_RADIO_AVS or radiotap data link type but wireshark is unable to change the airport extreme card to this mode and so is tcpdump using the -y option (the -L option only shows the ethernet dlt). Since I do not possess the necessary background working with these drivers could you please confirm that it is due to the latest update that I cannot capture using this dlt (perhaps there have been other cases like mine)? In the past I have done so but not since this last update. Yet, using the "airport sniff" utility in Terminal produces a pcap file with the appropriate IEEE 802.11 headers. Thank you in advance.

asked 13 Mar '11, 08:05

Vellerefond's gravatar image

accept rate: 0%

edited 13 Mar '11, 08:06

In Mac OS X, in order to get 802.11 headers, you must capture in monitor mode.

OS X 10.6 has libpcap 1.x; libpcap 1.x has an API to switch to monitor mode, supported on Linux, *BSD, and Mac OS X, and, on OS X, only allows you to select 802.11 headers if you've selected monitor mode.

The Wireshark 1.4.x 64-bit binaries for Mac OS X use the new APIs, so they do not let you select 802.11 headers unless you select monitor mode; if an interface supports monitor mode, there's a checkbox in the "Capture Options" dialog to capture in monitor mode. Check that check box, and it should offer you a choice of 802.11 headers with or without various radio headers.

The version of tcpdump that ships with 10.6, and the 64-bit binaries for Wireshark and TShark 1.4.x, also support a command-line option to request monitor mode - "-I" (capital-I). In order to capture with 802.11 headers with tcpdump, TShark, or, if you start the capture from the command line, Wireshark, you must pass the "-I" flag. That will automatically select 802.11 with radiotap if it's available, otherwise 802.11 with AVS if it's available, otherwise 802.11; you can use "-y" to choose link-layer headers other than the default.

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answered 14 Mar '11, 11:20

Guy%20Harris's gravatar image

Guy Harris ♦♦
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question asked: 13 Mar '11, 08:05

question was seen: 3,723 times

last updated: 14 Mar '11, 11:20

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