Ethereal-users: Re: [Ethereal-users] Capture format question

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From: Guy Harris <guy@xxxxxxxxxxxx>
Date: Wed, 25 Jun 2003 10:11:04 -0700

On Wednesday, June 25, 2003, at 9:56AM, James Fields wrote:

Many of my captures are from Distributed Sniffer Pro boxes.  I am using
editcap to convert them to libpcap format - but ntop doesn't seem to
like them.  I have also tried the other libpcap formats for Redhat and
so forth with no better luck.  Ntop reports it is opening a thread to
read packets from the file and then promptly closes the thread.

Closes the thread without reporting an error? I'd consider that a bug in ntop.

Ethereal can open those converted files just fine.

Can a version of tcpdump *built with the same version of libpcap as the one with which your ntop is built* read them? If not, what does it report?

HOWEVER - if I capture with Ethereal and save in libpcap format, ntop
can read those files fine.  So it seems there is something different
about a file captured with libpcap and saved that way as opposed to
something captured as a Sniffer format and converted,

There's something different about a file captured with libpcap and saved in that format, *with a link-layer type that the version of libpcap used in ntop can read*, and a file captured with a Sniffer and treated, by Ethereal, as requiring a link-layer type that the version of libpcap used in ntop *can't* read. I suspect that's the difference.

Another possible difference is that there might be a difference between Sniffer captures that include a CRC in the packet data and Ethereal captures that don't, but ntop *should* just think of the CRC as packet trailer data (as Ethereal would).