CyberCertPrepOT Security FundamentalsOT Fundamentals: Network Architecture & ProtocolsMEDIUMFree question
A vendor ships a PLC with Modbus/TCP Security enabled so that traffic is wrapped in TLS with mutual certificates. Which TCP port does the secured service use?
- A.TCP 802 registered for the secured variant
- B.TCP 4840 inherited from the OPC UA server stack
- C.TCP 443 reserved for the web management pages
- D.TCP 20000 borrowed from the DNP3 outstation listener
Why A is correct
The Modbus/TCP Security specification registers port 802 for the TLS-wrapped service, while legacy Modbus TCP stays on 502. Port 4840 is OPC UA, 443 is HTTPS, and 20000 is DNP3.
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