DNP3 over TCP/IP — Ethernet Transport Configuration
Key Takeaway
How to configure DNP3 over TCP/IP — port 20000, IP addressing, multi-master connections, keep-alive, and migration from serial to Ethernet.
Quick Answer
DNP3 over TCP/IP uses port 20000 by default (IANA registered). The outstation acts as TCP server; the master connects as TCP client. DNP3/TCP supports multiple simultaneous master connections and is the preferred transport for modern installations with Ethernet or cellular connectivity.
Port Configuration
The standard DNP3/TCP port is 20000. Some devices use port 20001 or other values. Ensure the port is open on firewalls between master and outstation.
Connection Model
- Outstation listens on TCP port 20000 (server mode)
- Master connects to outstation IP address and port (client mode)
- Multiple masters can connect simultaneously (device-dependent connection limit)
Keep-Alive
Configure TCP keep-alive to detect broken connections. Without keep-alive, a dropped connection may not be detected until the next poll timeout — causing unnecessary data gaps.
Migration from Serial to TCP
Many installations are migrating from serial/radio to cellular/Ethernet. DNP3 over TCP uses the same application layer — only the transport changes. Serial-to-Ethernet converters can bridge legacy serial outstations to TCP networks.
Security
DNP3/TCP over public networks (cellular, internet) should use VPN or Secure Authentication to prevent unauthorized access. See also OT cybersecurity best practices.
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Frequently Asked Questions
TCP port 20000 by default (IANA registered). Must be open on firewalls between master and outstation.
Yes. DNP3/TCP supports multiple simultaneous connections, though the exact limit depends on the outstation hardware. Most modern RTUs support 4-8 concurrent connections.
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