OPC FAQ

To configure OPC communication to pass through a firewall, you must open a port for DCOM communication and provide application exceptions. 

Configuration Procedure for Windows firewall (see below for hardware firewalls): 
 

1. OPC Client PC configuration: Provide exceptions for DCOM's end-point mapping (EPMAP) functions on TCP port 135. As well, provide exceptions for OPC Client applications.
    
2. OPC Server PC configuration: Provide exceptions for DCOM's end-point mapper (EPMAP) on TCP port 135. As well, must provide exceptions for both the OPC Server as well as OpcEnum.
    

DCOM will only require enabling the above ports to establish communication. DCOM will find these ports automatically. This method will only work with Win

DCOM can also be configured to pass information across static (or fixed) ports so it can work well with external or hardware firewalls. In this case, only 2 ports will be necessary.

OPCTI's Level 2: OPC Security and Level 4: Advanced OPC Projects cover this configuration extensively. For automated firewall configuration, refer to OPC Expert.