One of our customers currently experiences a strange performance issue. Basically, the problem is that the transfer of large files is slow when retrieving a large file from a server (Win2k3)that is connected on a gigabit interface to a workstation (Win-XP) on fast ethernet. For example a 130MB file can be uploaded in appr 12-15s, downloading it from the server takes about twice as long (31s).
The customer has all his servers attached to a 3750-stack, the workstations are on 3560-switches and the core is a redundant 6500. The exact network topology does not seem to make much difference though; I am also able to reproduce it on the 3750 stack by forcing a port to 100Mb and attaching a workstation to it.
There are no duplex mismatches in the network and the MTU size is 1500 for the whole network. Also, the gig-link on the server was not loaded, we used a dedicated testserver for our tests. Fiddling with the server's registry only produced worse results.
In the troubleshooting process, I already upgraded the IOS version of the 3750's from 12.2.25 to 12.2.40 but this made no difference. Also, the complaints have started after we installed the 3750 stack.
To add to the weirdness of this, the customer reported that the problem was not present on workstations running Vista or Linux. That was where I stopped investigating a month ago and I considered the issue a non-Cisco problem. Unfortunately we have just been informed that the problem is also absent when the switch is a 3Com instead of a 3750. My impression is that it might be related to packetbuffering but I find the issue very hard to troubleshoot.
I will go to the customer next week to make some traces but any input from anyone of you is highly appreciated.