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Citrix NetScaler: Protocol Driver Error

Today I have been troubleshooting a Citrix NetScaler configuration, where some clients received the Protocol Driver Error message when executing a published application. This error message is mostly related to a wrong configuration of the Security Ticket Authorities (STA’s). I spent a lot of time troubleshooting this issue and focused on the STA configuration. I have been deleting, adding and modifying multiple STA’s to the configuration of the NetScaler without any luck. I checked the configuration of the firewall, but this wasn’t the problem either.

I decided to go back to basic and just added one STA to the Virtual Server and the STA service group used by the Web Interface. I was able to login with that STA server, but after a while I wasn’t able to login and received the Protocol Driver Error again.

While browsing through the NetScaler I noticed one thing. Every time I wasn’t able to login, there were 5 concurrent users already connected with the NetScaler. I did some more research on the internet and found the following article.

Reading the article, tells me that, by default, only 5 concurrent ICA sessions are possible through the NetScaler. I checked the license and the customer has a license for 50 SSL VPN connections, like shown below:

> show license
License status:
Web Logging: YES
Surge Protection: NO
Load Balancing: YES
Content Switching: YES
Cache Redirection: NO
Sure Connect: NO
Compression Control: NO
Delta Compression: NO
Priority Queuing: NO
SSL Offloading: YES
Global Server Load Balancing: NO
GSLB Proximity: NO
Http DoS Protection: NO
Dynamic Routing: YES
Content Filtering: YES
Integrated Caching: NO
SSL VPN: YES  (Maximum users = 50)
AAA: NO
OSPF Routing: NO
RIP Routing: NO
BGP Routing: NO
Rewrite: YES
IPv6 protocol translation: YES
Application Firewall: NO
Responder: YES
HTML Injection: NO
NetScaler Push: NO

I increased the default value to 50 with the following command:

> set aaa parameter -maxAAAUsers 50

From that point on I was able to start another ICA connection, while there were already 5 concurrent users connected. Now I have to wait and see if this actually solved the problem, but I guess it has.

I tried to increase the –maxAAAUsers value to a value higher than 50, but that isn’t possible as you can see.

> set aaa parameter -maxAAAUsers 100
ERROR: MaxAAAUsers value not allowed by license

Citrix Access Gateway: duplicate STA ID

I received complains from a customers who wasn’t able to add two new Citrix servers to his Citrix Access Gateway configuration. He could successfully add the first Citrix server, but he couldn’t add the second Citrix server, because the first was overwritten by the second. I looked at the problem and noticed that both Citrix server were using the same STA Identifier.

After asking some question about the installation of the Citrix server, I discovered that the second Citrix server was a clone of the fist Citrix server. That is why both servers have the same STA Identifier. The STA ID from a Citrix server can be changed by altering the file CtxSta.config. By default a Citrix server has two CtxSta.config files, located at the following destinations (default installation):

  • C:\Program Files\Citrix\System32;
  • C:\Inetpub\Scripts;

I had to change the STA ID in the C:\Inetpub\Scripts directory, because IIS was used to share port 80 on the server. The CtxSta.config file contains a UID, like the example below:

[GlobalConfig]

UID=STAA3D2D2970C9C

TicketVersion=10

TicketTimeout=100000

MaxTickets=100000

LogLevel=0

MaxLogCount=10

MaxLogSize=20

LogDir=c:\inetpub\Scripts\

; Allowed Client IP addresses
; To change, substitute * with client IP addresses. Use ";" to seperate IP addresses/address ranges.
; To specify a range of IPs always use StartIP-EndIP.
; For example, AllowedClientIPList=192.168.1.1;10.8.1.12-10.8.1.18;123.1.2.3

AllowedClientIPList=*

; SSL only mode
; If set to on, only requests sent through HTTPS are accepted
SSLOnly=off

I changed the UID on the second server and restarted IIS. I tried to add the Citrix server to the Citrix Access Gateway, which is now possible with the new unique STA ID. The last step is adding the second Citrix server to the Citrix WebInterface (server farm & STA ID).