Catalyst 3524 - Capturing fragmented packets

Unanswered Question
Nov 20th, 2008

Greetings,

I have run into an interesting issue with a trunked connection to my ASA.

Scenario: ASA-5510 connected to a Catalyst 3524 switch via a dot1q trunk. There are approximately 12 vlans configured and passing traffic.

The ASA interface shows no errors; the Catalyst switch is incrementing runts fairly rapidly.

From what I have read this typically is a cabling or hardware issue. We changed ports and cables on the Catalyst switch to rule out that side. Both ASA and Switch are set to Full Duplex/ Speed 100.

From a troubleshooting perspective, I am limited on my packet captures due to the switch and/or my NIC hardware discarding 'bad' packets. I don't have access to a hardware packet capturing device or a NIC with that capability.

To anyone's knowledge, is there a way to capture the packets being dropped at the switch port? I have a port monitor set up and have disabled "checksum offloading" on my NIC; so far that is the best I have come up with.

It looks like the switch will increment the runts counter, but not log any of that info.

I am eliminating any other port issues I see on the switch, but that hasn't made a difference so far.

My apologies for the long post, but I do appreciate your patience and expertise!

Thanks for your time!

I have this problem too.
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drolemc Thu, 11/27/2008 - 10:53

Use below command to capture fragmented packets.

Switch# Show cdp traffic

This command will displays total no fragmented packets

rholdsrdh Mon, 12/01/2008 - 05:13

Thanks for the info - I will be able to use that for future troubleshooting!

I have resolved the incrementing runts issue with an IOS upgrade on the switch (to current level for the Cat 3524).

After the upgrade, the counters no longer increment. I was hoping this would be the case; we were just waiting for a maintenance window to complete the upgrade.

Thanks again!

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