[olug] Switch port errors...

Trent Melcher trentm at q.com
Tue Jul 27 20:21:12 UTC 2010

Can you hard set the duplex and speed on the cable modem?  Sounds very much
like a speed/duplex mismatch.  Possibly change the port on the switch that
is plugged into the cablemodem to auto/auto for speed and duplex.


-----Original Message-----
From: olug-bounces at olug.org [mailto:olug-bounces at olug.org] On Behalf Of Dan
Sent: Tuesday, July 27, 2010 1:24 PM
To: Omaha Linux User Group
Subject: [olug] Switch port errors...

I'm still diagnosing my Cox Cablemodem port errors issue....  It's a case of
"Windows is fine" but everyone else is complaining!

Here's my setup:

Cisco 2900XL port 23 ==> Cox Cable Modem (Motorola Surfboard SB5101U)
(Crossover from modem to switch port)
Cisco 2900XL port 22 ==> Linux firewall
Cisco 2900XL port 21 ==> unused
(All three ports are in the same VLAN)
All speed tests were performed to www.speedtest.net using "Dallas".
The Cisco and Linux interfaces are set to 100/Full -- didn't pursue that
with the laptops yet.

We plugged a Windows system directly into my cablemodem ethernet port, then
ran speed tests to the Omaha cox server and got 30Mbit/sec downloads and
6.5Mbit upload speeds (I have their new SOHO 25/5 package).  We swapped out
cablemodems and used their tester modem and it too got 30/6Mbit.

When we put their laptop onto port 22, then power-cycled the cablemodem
their speeds were ~1.8Mbit and 6Mbit down/up respectively (YES, less than 2
Mbit DOWNLOAD speed just through the switch).

Before running the test through the switch I did a "clear counters" to reset
the error counters.  After running the test (~15 seconds total), I see this:
SW001#sh int fas 0/23
  Output queue 0/40, 0 drops; input queue 0/75, 0 drops
  5 minute input rate 153000 bits/sec, 43 packets/sec
  5 minute output rate 97000 bits/sec, 27 packets/sec
     4775 packets input, 4929578 bytes
     Received 226 broadcasts, 0 runts, 0 giants, 0 throttles
*     99 input errors, 41 CRC, 58 frame, 0 overrun, 0 ignored*
     0 watchdog, 1 multicast
     0 input packets with dribble condition detected
     4661 packets output, 3039483 bytes, 0 underruns
*     0 output errors, 0 collisions, 0 interface resets*
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier
     0 output buffer failures, 0 output buffers swapped out

If I plug the cablemodem straight into my Linux firwall, or into my laptop
running Linux, both see the input errors (from the modem) on the ethernet
port so I doubt it's a bad NIC or switch port.

My next steps:
 * Replace the cables
 * Move to new switch ports just in case.
 * Replace the firewall NIC
 * Test using my old cablemodem (Surfboard SB5101) on my @Home service.
 ** Move my old cablemodem to the SOHO service and see if speed changes.
 * Use a sniffer and setup port spanning on the cablemodem side.
 * Research how to get better diagnostics out of the Surfboards.

Any other suggestions?
I'm pulling my hair out on this one...and I don't have that much left!


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