[Lvlug] Jabbers, Jabbers but where?

[dann]

Okay, I cannot get a solid answer on this problem.

About a month ago, while diagnosing a possibly unrealated problem with
cisco, we noted an increasing number of collisions on our catalyst port
going out to the internet.  This port was originally set up as a 100
Half-duplex connection to a 3com 3300 switch also set up for 100 HD that
connects our ATM to the IU (our ISP).  Running at HD, you would expect to
see some collisions, but the counter was increasing dramatically.  Cisco
recommended we switch over to FD to remedy the problem.

I did that and soon learned that the cross-over cable was not a fd cable. 
I created a new cable and thought I was good to go.

About an hour later, we lost connectivity to the internet.  The catalyst
port reported that it was connected, but I could not reach the 3com
switch.  I noted there were a number of FCS (Frame Check Sequence) errors
and Runts.  Another diagnostic screen showed that the Receive buffer was
filling up and dropping packets.    

Cycling the port brought it back and I was able to view the 3com
statistics.  The port connected to the catalyst reported CRC (Cycle
Redundancy Check) errors and Jabbers. 

This problem would happen every few hours.  Eventually I learned that
connectivity would come back on its own after a few minutes.

Over the past few weeks I have learned that these errors could be a result
of faulty hardware or cables.  I have replaced the cable and tried three
different ports on the 3300 and 2 different ports on the catalyst.

The other day I found another cisco diagnostic utility that indicated
during these periods that the catalyst port was reporting jabbers also.

So here is what I suspect is happening.  The catalyst and 3300 are
receiving jabbers, but the 3300 has a lower threshold which is
auto-disabling the port until either the jabbers subside and/or a certain
time out is reached.  When the port closes, the catalyst cannot forward
our internet traffic and the receive buffer fills.  Thus, packets are
dropped resultingin the In-Lost errors.

My question has been this.  Should I be looking to the 3300 or the
Catalyst as the device jabbering?  Or is it possible that there is a third
device out there (either on our network or somewhere on the IU's) with a
jabbering NIC.  If there is a device with a jabbering NIC, should I not
see this jabbering on the port the device is connected in to?

Anyone with some advice?

I have tried sniffing packets to the port, but I never luck out to be
monitoring when the problem occurs.  I get to see all those students
sneaking AIM (can read all this clear text messaging).  I have not noticed
any jabbering during my sniffs.


By the by, using FD resolved the collision errors on the catalyst.

-- 
Daniel S. Washko
Lehigh Valley Linux Users Group
www.thelinuxlink.net/lvlinux
get slack (www.slackware.com ) and get happy