OPC through a firewall - How?

Hi,

I am having a problem when connecting my WinCC 6.1 as a OPC DA client to WinCC OPC Server. I have a Scalence S612 firewall there between the server and clientto isolate the WinCC OPC server machine from the rest of the network.

OPC is using DCOM protocol, which seems to use different TCP ports (not fixed one). So I can not "drill a hole" to the firewall. Without the firewall the connection is tested to be ok.

What should I do? Is there a solution available without having to change i.e. to OPC XML?

Rauno