OPC uses DCOM to communicate between computers. DCOM is subject to several security restrictions so you may have problems using DCOM with firewalls or to communicate between computers which are on different domain servers.
Because DCOM authentication and communication is restrictive, several companies have created products that allow you to use OPC but bypass DCOM through the use of tunneling software. This third party software is installed on both the OPC client and OPC server machines and the OPC data is passed between the computers not using DCOM.
For more information and to find third party tunneling software applications, please visit the OPC Foundation website:
<http://www.opcfoundation.org/>
