odd SPAN problem

Unanswered Question
Feb 14th, 2008

I'm installing a Data Discovery appliance soon and during testing noticed it was only seeing one side of an MSN messenger conversation. I plugged in a laptop directly to the switch and ran tcpdump. Sure enough I saw SYN and ACK, but no SYN/ACK in between. Although strangely enough the whole conversation was in the MSN client.

I then checked to make sure that on the 3750 it was monitoring both directions. It was configured for both directions. Everything checks out correct but I still only see one side of the conversation. It occurred to me it may have something to do with VLANs but that looks good as well.

Any suggestions? Thanks.

I have this problem too.
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royalblues Fri, 02/15/2008 - 03:43

This can happen when the NIC card on the desktop used for spanning cannot run properly in promiscuous mode and does not capture all the packets

Have a look at this forum thread





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