I was not meaning the 14-byte Ethernet header. And yes, it usually is
the hardware's job to attach the preamble as is my understanding too.
But, the equipment I am using has the capabilities to not attach a
preamble and let the user define there own. It is a nice feature for
testing purposes, but I didn't have the full specs on it and was not
defining something correctly and thus it lead to two preambles.
Pete
-----Original Message-----
From: wireshark-users-bounces@xxxxxxxxxxxxx
[mailto:wireshark-users-bounces@xxxxxxxxxxxxx] On Behalf Of Guy Harris
Sent: Thursday, March 29, 2007 11:49 AM
To: Community support list for Wireshark
Subject: Re: [Wireshark-users] Seeing Preamble in Decodes
On Mar 29, 2007, at 12:18 AM, Gross, Pete wrote:
> I was able to figure out that for some reason the hardware was
> attaching its
> own preamble
I think it's almost always the job of the hardware to attach the
preamble.
Now, if by "preamble" you mean, for example, the 14-byte Ethernet
header, that's a different matter; that's not the "preamble" in
Ethernet. That's usually attached by the software, although if the
adapter directly supports VLANs it might take your packet, strip off
the Ethernet header, use the destination and source addresses of that
header and the VLAN Ethertype to make a new 14-byte Ethernet header,
and put the type field from the Ethernet header into a VLAN header.
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