Hi Selçuk, if you're doing anything involving multiple link types and
Wireshark/dumpcap, you'll want to check out the enhanced pcap-ng file format
support in the latest SVN versions of Wireshark. So it seems, mergecap
doesn't support merging multiple link-layer types in pcap-ng files yet,
although as a workaround, you can concatenate the files (dumped with dumpcap
-n) in order of date/time created, and receive a usable result.

Otherwise, if you ended up with a "cooked" capture file (as produced by
capturing on the Linux "any" pseudo-device), you'll only get useful data
from some of the packets.

As with the pcap file format, I believe that the pcap_* APIs only let you
work with one link-layer type at a time, although others are free to correct
me on that, since I haven't worked with them directly.

I hope that helps,
Tyson.

On Fri, May 29, 2009 at 1:23 PM, Selçuk Cevher <[email protected]> wrote:

> Hi Everybody,
>
> First of all, I am not sure if this is the right place to ask this
> question.
>
> How can I determine the protocol running on data link layer (i.e.,
> Ethernet, Wi-Fi 802.11, etc) while analyzing packets in a "merged" dumped
> file with pcap format if the pcap file contains a mixture of packets with
> various data link layer protocols ?
>
> libpcap has pcap_datalink(...) function allowing us to determine the data
> link layer protocol for live capture -- it gets this information directly
> from the actual network interface that is sniffed on.
>
> However, in the case of offline analysis, it seems pcap_datalink() will
> not work since it is not possible to know what kind of interface those
> packets came from.
>
> Any idea ?
>
> Thanks.
>
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