Switch working like a hub

[fpiedrafit]

We have a four members stack of Catalyst 3750G 24PS (IOS 12.2.25-SEE). Every certain time all the lights of the ports belonging to same vlan begin to blink very quickly and simultaneously (These ports are in a voice vlan too). Plugin a sniffer in one of this ports I can see all traffic of both vlans (normal and voice vlan). Users notice some little splits in communications but CPU and MEM of switches stack remain low. Traffic in the trunk line what connect to distribution switch is normal. An this just happens in this stack, others stacks in our networks don't have this problem using similar configurations.

Any idea will be welcome

Thank you in advance

[Roberto Salazar]

Waht kind of traffic are you seeing on both vlans. Also, you said ports have voice vlan and data vlan and your sniffer trace shows traffic for both the voice vlan and the data vlan, it's normal to see both traffic in the port taht belongs to those vlan. What you need to verify is what kind of traffic and if the traffic seen is a unicast that does not belong to that port.

[fpiedrafit]

Sorry bosalaza but I didn't explain very well the problem. In any port of the stack I can see traffic destined to the same vlan of the port but not destined to the device attached to it.

I already know what it is happening. We have an asymmetric roting problem. We are using HSRP in ours two core switches and some traffic is being flooded unnecessarily to some ports of the same VLAN.

Here is the cisco explanation of the problem:

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00801d0808.shtml

We are happy for having found a logical explanation to the problem, because it'was a little crazy to try to undestand what it was happening at first sight. Now it will be easier to look for a solution.

Best regards