[nsp] another counter funny

[Christopher J. Wolff]

Gert,

I didn't have the time or motivation to open a CSI investigation into
interface counters.  I offer this observation to try to help you diagnose
this phenomenon, as many others on this list have helped me tremendously in
the past.  

Regards,
Christopher J. Wolff, VP CIO
Broadband Laboratories, Inc.
http://www.bblabs.com

> -----Original Message-----
> From: Gert Doering [mailto:gert at greenie.muc.de]
> Sent: Wednesday, April 28, 2004 8:52 AM
> To: Christopher J. Wolff
> Cc: 'Gert Doering'; 'Benjie Ko'; cisco-nsp at puck.nether.net
> Subject: Re: [nsp] another counter funny
> 
> Hi,
> 
> On Wed, Apr 28, 2004 at 08:38:28AM -0700, Christopher J. Wolff wrote:
> > I set a full/100 port on a cat 3550 for connection into a Nortel BPS.
> > Unbeknownst to me, the Nortel BPS port was set up as auto detect.  The
> > Nortel autodetected that the cat 3550 port was half/100.  There were
> many
> > collisions recorded on the cat 3550 port counters.
> 
> How can the 3550 detect a collision here?  If the 3550 is set to
> "full-duplex", a collision (on the 3550 side) *can* *not* *happen*.
> The very essence of a "collision" (reception of a packet preamble while
> preparing to send) cannot happen if the port is *permitted* to send and
> receive at the same time (= full-duplex).
> 
> The Nortel will report collisions to no end (because every packet sent
> full-duplex by the 3550 will be seen as a collision).
> 
> gert
> --
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> Gert Doering - Munich, Germany
> gert at greenie.muc.de
> fax: +49-89-35655025                        gert at net.informatik.tu-
> muenchen.de