Intermittent Thin Client disconnects

We recently had a problem after a Citrix rebuild where we were seeing thin clients intermittently disconnect from the citrix servers. Nothing in the event logs, just a lovely error on the Thin Client (Igel) reporting a Driver protocol error. The users could immediately reconnect, but 10-15 disconnects a day was getting a bit annoying for poor Joe Soap.

The problem was very difficult to track down due to absolutely no logging or even acknowledgement of the problem in any event logs.

We found that the reinstall was enabling the advanced IP features in Windows server 2003 involving TCP Offloading from the Nic to the CPU, Citrix and particularly thin clients do not like this feature one bit.

To disable these options, enter the following keys into the registry and reboot.

[HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTcpipParameters]
“EnableTCPA”=dword:00000000
“EnableRSS”=dword:00000000
“EnableTCPChimney”=dword:00000000

On a side note, I’ll be disabling these keys going forward on all server builds, its not a nice feature to implement unless the application is aware of the offload.

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