ICS / OTTCP/UDP 20000 Cleartext by default
Port 20000: DNP3
DNP3
Distributed Network Protocol, widely used in electric and water utilities between control centres and outstations.
How attackers abuse it
- Spoofed or replayed commands to field devices where Secure Authentication is not used.
How to defend it
- DNP3 Secure Authentication where supported.
- Segmentation and protocol-aware monitoring.
Exam tip
DNP3 is common in utilities; Modbus in general manufacturing.