The QlikView QVP (4747) protocol and Tunneling

The QlikView Server uses port 4747 and the QlikView QVP protocol to communicate with other services, as well as directly with clients using the Internet Explorer Plugin or QlikView Desktop.

For an overview on where the QlikView Protocol is used, please reference the QlikView Help site. 

When the port 4747 is not available, communication with, for example, the Distribution Service or WebServer is not possible. End Users may then also see connections failing when attempting to open .qvw documents on the AccessPoint using the Plugin or Desktop Client. 

Can port 4747 be changed? Port 4747 cannot be changed. 

Possible symptoms include (but are not limited to):

• Failing tasks (Distribution errors)
• Users unable to use Internet Explorer Plugin or Desktop Client
• Internet Explorer Plugin Desktop Client are unusually slow
• WebServer reports No Server on AccessPoint

Example error messages from QlikView Distribution Service to the QlikView Server:  

Warning    Could not connect to QVS. QVS=qvp://<Server Name>

Example error message from QlikView WebServer to the QlikView Server:
Example message in the QlikView WebServer when port 4747 is blocked from client to server, but otherwise available between the services:

Request received [GET]: http://localhost/QvPlugin/opendoc.htm?document=allocation performance.qvw&lang=en-
Information    Request received [POST]: http://localhost/scripts/QVSTunnel.dll?host=qlikserver1
Information    Tunnel-request:  || <QVS
Information    Tunnel-response:

 

Plugin and Desktop Client only: A Firewall or Proxy is blocking port 4747 and cannot be reconfigured

If port 4747 is not available, the Internet Explorer Plugin and Desktop Client will automatically attempt to switch to tunneling. Tunnel communication packages the communication into a port 80 (or 443) tunnel. While communication is then possible, performance will be impacted substantially.

Tunnel communication is automatically configured for the QlikView WebServer.
For Microsoft IIS see How To ConfigureTunneling Using Microsoft Internet Information Server (IIS)

It is recommended to ensure port 4747 is made available for all clients, or to otherwise switch users over to use the Full Browser Client. 
One other possibility is to check filenames for special characters and remove those to see if that addresses things too.  The thought is when having to tunnel a connection, the special characters in the filename may cause a problem in the URL encoding.