I have a Cisco 3825 router running 12.3(11r)T1

It originally had a single 4ESW switch module inserted into it. The customer likes each VLAN to have its own interface for routing. The customer currently has 4 VLANs and required the addition of another VLAN. For other customers I would normally use a trunk from the core switch to the router and just add the additional VLAN but as this customer insists on a spearate physical port for each VLAN. They supplied another 4ESW module.

I added the second 4ESW and linked them together using a cable. I had to move one of their existing VLANs from the origianal 4ESW to the new 4ESW to free up a port to connect the two together.

The VLAN I moved to the new 4ESW had some servers on. (VLAN 999)

See config below showing the stacking partners defined on the two cards.

interface FastEthernet0/0/1

description stack link to f0/1/3

switchport stacking-partner interface

interface FastEthernet0/1/3

description stack link to f0/0/1

switchport stacking-partner interface

As soon as I moved VLAN 999 to the new 4ESW the customer began to complain about server file transfer performance from all VLANs to and from VLAN 999. I did some testing and proved that the data rate was about 1/10th of what is was when the server VLAN 999 was on the original 4ESW. I moved the VLAN back to the original 4ESW and the data transfer rate went back to its original rate.

Anyone got any ideas of why this would be occuring. I checked the physical and virtual interfaces and there were no errors or indications to why performance should be degrated.

Thanks

Barry