Archives for April 2009

Pulling your hair out over network slowness?

So today I received a request for assistance from another project on a very peculiar problem their system was experiencing. They were deploying a new version of their system and the ‘go live’ date was fast approaching. Their thin client architecture relies on a Citrix server and during some final testing they were experiencing some odd logon delays.

During the first Citrix or RDP session to their application servers the logon time, which is normally a few seconds, was extending into minutes. Killing the session and re-connecting ‘fixed’ the problem and logons were back to a few seconds. But use a different thin client, and the problem reappeared. Or wait 20 minutes between sessions and the symptoms reappeared. Whooah?!!?

After several hours of working with them on the problem, I noticed a trend forming. The problem manifested itself only when connecting from a Windows XPe client to a physical Server 2003 SP2 machine. The logon delay was not present on Server 2003 SP1 or Windows 2000 servers, nor server 2003 SP2 virtual servers running on ESX.

During my previous job as a senior consultant I ran into similar situation with server 2003 SP2 on some new servers. The problem? In Windows Server 2003 SP2 Microsoft enabled a feature called Scalable Network Pack (SNP). This ‘enhancement’ enables some offloading of network functions into the NIC, to help with CPU utilization. BUT, many NICs exhibit odd problems with this feature enabled. Symptoms can be all over the map, but the commonality is that behavior seems erratic and hard to track down.

The solution? Install microsoft patch KB948496. It’s not a security patch, so if your systems aren’t connected to the internet and get Windows Updates on a regular basis, your machines may not have it installed. I HIGHLY recommend all physical server 2003 SP2 machines get the patch applied. While Microsoft’s intent with SNP was well intentioned, I think it has created more problems for customers than it has solved.

So if your physical server 2003 SP2 systems are behaving oddly and they don’t have the SNP patch, install it and see if your problems are cured.