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// IoT & industrial (ICS)

Port 19999: Distributed Network Protocol - Secure

Port 19999 is assigned by IANA to dnp-sec (Distributed Network Protocol - Secure).

19999

How dnp-sec works

IoT & industrial (ICS)
controllerPLCdnp-secno authentication controllerPLCdnp-secno authentication

A controller sends commands to an industrial device on port 19999, which acts on the physical process.

Transport
TCP · UDP · SCTP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
IoT & industrial (ICS)
01 Security

Is port 19999 dangerous?

We have no specific security note for port 19999. Its risk depends on the program actually listening on it. General advice for iot & industrial (ics) services:

  • Industrial and IoT protocols often have no authentication: never expose them to the Internet.
  • Segment OT networks from IT and use protocol-aware firewalls.
  • Monitor with an ICS-aware intrusion detection system.
02 Registry

IANA registry entries for port 19999

ServicePortTransportDescriptionReferenceUpdated
dnp-sec 19999 TCP, UDP, SCTP Distributed Network Protocol - Secure - 2008-08-04

// source: IANA service name and port number registry

03 Check it

Which program uses port 19999, and is it reachable?

Linux

sudo ss -ltnup 'sport = :19999'      # process listening on 19999
sudo lsof -nP -i :19999

macOS

sudo lsof -nP -i :19999

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 19999 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 19999
netstat -ano | findstr :19999

From another machine

nmap -p 19999 -sV <host>
sudo nmap -sU -p 19999 <host>
nc -zv <host> 19999

Block it in the firewall

sudo ufw deny 19999/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 19999" -Direction Inbound -LocalPort 19999 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 19999 used for?

Port 19999 is assigned by IANA to dnp-sec (Distributed Network Protocol - Secure).

Is port 19999 TCP or UDP?

Port 19999 is registered for TCP and UDP and SCTP.

Is it safe to open port 19999?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Industrial and IoT protocols often have no authentication: never expose them to the Internet.

How do I check if port 19999 is open?

On Linux run "ss -ltnup 'sport = :19999'", on macOS "lsof -nP -i :19999", and on Windows "netstat -ano | findstr :19999" to see the local process. From another machine, "nmap -p 19999 <host>" shows whether it is reachable.

05 Related
:1883 MQTT tcp · udp · high risk :8883 MQTT over TLS tcp · udp · moderate risk :502 Modbus TCP tcp · udp · critical risk :102 Siemens S7 (ISO-TSAP) tcp · udp · critical risk :47808 BACnet udp · tcp · critical risk :20000 DNP3 tcp · udp · sctp · critical risk :44818 EtherNet/IP tcp · udp · critical risk :802 Modbus Application Protocol Secure tcp · udp

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