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TCP 4840

ProtocolTCP
Port4840
LabelsOPC UA Connection Protocol (TCP) and OPC UA Multicast Datagram Protocol (UDP) for OPC Unified Architecture from OPC Foundation

Synopsis

  • TCP port 4840 is the well-known port for OPC UA (OPC Unified Architecture) using the UA-TCP binary protocol (IANA service name: opcua-tcp).
  • Siemens SIMATIC S7-1500 and ET 200SP CPUs expose their integrated OPC UA server on port 4840 by default.
  • Beckhoff TwinCAT 3 OPC UA Server listens on opc.tcp://:4840 by default.
  • CODESYS OPC UA Server (part of many PLCs running the CODESYS runtime) uses 4840 as its default endpoint port.
  • Omron NX/NJ series PLCs provide an integrated OPC UA server that commonly defaults to TCP 4840.
  • Many open62541-based OPC UA servers and vendor/demo servers (e.g., Unified Automation sample servers) default to 4840 for testing and deployment.
  • OPC Foundation and industry interoperability test setups frequently use opc.tcp endpoints on 4840 during plugfests and lab environments.
  • Security note: attackers routinely scan 4840 to find exposed OPC UA servers in ICS/OT networks; multiple historical OPC UA stack vulnerabilities and frequent misconfigurations (no encryption/authentication) have enabled information disclosure or denial-of-service against services on this port.

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