odd SPAN problem

[jourden.parks]

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.

[royalblues]

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

http://forums.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Unified%20Communications%20and%20Video&topic=IP%20Telephony&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.2cbf0117/8#selected_message

HTH

Narayan