[Guy Harris <gharris@xxxxxxxxx>]

mark.dixon wrote:
> I'm looking to capture HDLC packets between two CISCO routers.

If that's "Cisco HDLC", then

	1) it's not really HDLC in the full sense of the word (no "control" 
field, for example) - it's probably just using the low-level 
bit-stuffing and framing of HDLC;

	2) Ethereal can already dissect it;

	3) if you can run Ethereal (or Tethereal or tcpdump) on a machine 
that's an endpoint of the CHDLC traffic (which, if it's a Cisco router, 
you probably can't), you might be able to capture on an interface that's 
a source or sink of the traffic, if the OS supports it ("endpoint" here 
doesn't mean, for example, IP-layer endpoint, as the router probably 
turns some of the traffic into Ethernet traffic and processes other 
traffic, such as SLARP, internally);

	4) otherwise, you might be able to use an Endace DAG card to do 
"third-party" passive capture of the traffic, if your OS supports that 
(they support Linux and possibly also FreeBSD and Windows).