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One way traffic appearing flooding network interfaces

Hello Everyone,

I have a perculiar issue occuring on a Cisco network comprised of legacy switching equipment:

Core Switches          2 x 3550-12G

Edge Switches         5 x 2950G-48-EI Gigastacked split across the two cores via fibre

I have servers connected on VLAN 20, and I have users on VLAN 91. What I am seeing is one-way conversations from the server VLAN to the user VLAN on and interface which is not orginating the requests. The traffic looks like it is broadcasting across VLAN 91 however the traffic in question is not broadcast traffic.

All switches are now on the latest code available for them.

I considered that this could have been spanning-tree topology changes causoing momentary flooding on the VLAN, however I cannot see any spanning-tree topology changes on the VLANs.

The server VLAN (20) also connects to a HP Procurve switch to a remote site, and I'm not sure if this could cause the issue.

Has anyone seen anything like this before?


Toby McMichael


Re: One way traffic appearing flooding network interfaces

Sounds like you could be spanning vlans 19 & 20. Make sure that your uplinks & redundant servers are all on the same VLAN (or better yet trunk them).