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Grey screen sometimes on one XenApp Server for all users connecting to it

Kevin Vlasselaer


Hi Everyone,


Sometimes there's one XenApp server between others in the same Delivery Group with the same Snapshot that's giving a Grey screen for all the users connecting to it. 

Users launching the "Desktop", get the Citrix Frame but with a "blank" grey screen. The screen stay opened but no pictures, mouse or anything displayed on it.


After a little debugging, I noticed that the connections made on this particular problematic XenApp server are no more in UDP but in TCP (fallback i suppose).


So I used the "HDX Adaptive Transport" policy to make some test and.. I get very strange results


1) When I force EDT (Diagnostic Mode) and make a new connection on the server --> I get two errors frames :

         --> "The Connection to Desktop failed with status (Unknown client error 0)"

          --> "Unable to connect to the server. Contact your system administrator with the following error: SSL Error 31: The operation completed successfully."


2) When I force TCP (OFF mode) and make a new connection on the server             

            --> The citrix frame just pop and disapear instantly (no error message shown)

            --> In Director the error is : "A session has been reported as terminated from the VDA after the client has initially contacted the VDA but before it completed the connection sequence"


3) When I force in automatic (Prefered Mode)

            --> Same behaviour as the TCP mode (No error message Shown and error in director) --> But if I reboot, session are working great again.


There's obviously a network problem (I asked an access to the firewall) but what I don't understand is that if it's TCP the problem, then when I force EDT it will normally work.. and if it's UDP that's not correctly configured, the forced TCP would normally work. In the current situation, when I force one or the other type, it's not working. But if I choose "Prefered", the connections are working...
Normally the "prefered" option just try EDT and if it's not working, it fallback to TCP. Obisously again, the "Prefered" option make another change and I would like to know what kind of difference it's that make it working.


Thanks for your enlightenment !


Informations : 
Test connections are done in LAN (not through Netscaler)
Version of Citrix infrastructure is 1912 LTSR CU3

Session reliability is enable

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