Ethereal-users: RE: [Ethereal-users] vlan

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From: <buercky@xxxxxxxxxxx>
Date: Tue, 21 Feb 2006 19:59:51 -0600
thanks Guy 

sniffer trace im using just ethereal as my tool no other.
my pc does have QOS on the nic card able to be enabled and is.  I was able to find a cap with the vlan tagging in it on the website and my cap does not get that field. so I was wondering  

how do you know whether you are getting the tag / ID   or not...?  
            we are trying to  use this as a tool for VOIP and determine if VLAN is on or off and prove it to our customers.


is there a way to assign a vlan id # in a pc?  (windows)or is it done only on the layer 2 switch
 

-----Original Message-----
From: ethereal-users-bounces@xxxxxxxxxxxx
[mailto:ethereal-users-bounces@xxxxxxxxxxxx]On Behalf Of Guy Harris
Sent: Tuesday, February 21, 2006 6:09 PM
To: Ethereal user support
Subject: Re: [Ethereal-users] vlan


Mix (E-mail) wrote:
> where do I need to look in the sniffer trace for the VLAN ID or TAG value
> I can see the DSCP tag but cant find the VLAN ID or TAG

"Sniffer trace", in the sense of a trace captured with Network
Associates/Network General's Sniffer(R) product, "sniffer trace" in the
sense of a trace you captured with Ethereal (or tcpdump/WinDump), or
"sniffer trace" in the sense of a trace you captured with some other
application?

A packet with a VLAN tag will probably have an Ethernet header, which
should have a destination and source address and an Ethernet type value of
hex 8100, followed by a VLAN header, which includes the VLAN tag and a
type/length value.

If it doesn't have the VLAN header, and has an Ethernet header with an
Ethernet type value other than hex 8100 (for example, hex 0800 for an IP
packet), then some of the hardware or software Ethereal uses to capture
the packets stripped off the VLAN header before handing the packet to the
capture application, so it's not there.

If you were capturing with Ethereal (or tcpdump/WinDump or some other
libpcap/WinPcap-based application), and didn't get VLAN headers, see

    http://www.ethereal.com/faq#q7.11

and the Ethereal Wiki item to which it refers.

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