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.
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.