A is correct answer.
OPC Classic relies on Microsoft's Distributed Component Object Model (DCOM) and Remote Procedure Call (RPC) technologies, which dynamically assign TCP ports for communication between OPC clients and servers.
DCOM/RPC can use any port number within the range of 1024 to 65535, meaning that a firewall would need to be configured to allow traffic on a vast number of ports, creating a significant security risk.
The dynamic nature of OPC Classic's port usage makes it difficult to implement effective security measures with traditional firewalls, as they cannot be configured to allow traffic only for specific applications or services.
OPC UA (OPC Unified Architecture) is a more modern and secure alternative to OPC Classic, as it uses a more predictable and secure communication protocol, making it easier to configure firewalls and implement security measures.
OPC Classic relies on Microsoft DCOM (Distributed Component Object Model) for communication. DCOM dynamically assigns ports for communication within the range 1024 to 65535, which makes it firewall-unfriendly
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