Port 20000 (DNP3)

Distributed Network Protocol 3 for electric and water utility SCADA. Usermin also defaults to 20000.

Registered (user) port, 1024-49151 TCPUDP Industrial control (ICS/SCADA) Do not expose to the internet

What port 20000 is used for

Distributed Network Protocol 3 for electric and water utility SCADA. Usermin also defaults to 20000.

Do not expose to the internet. Utility control traffic must stay on isolated networks; use DNP3 Secure Authentication where supported.

Service nameProtoDescriptionAssigneeReference

dnp TCP DNP Michael Thesing -

dnp UDP DNP Michael Thesing -

dnp SCTP Distributed Network Protocol DNP Users Group -

Registry dates for this port: registered 2022-12-20.

Linux: is anything listening on TCP 20000?

sudo ss -tlnp 'sport = :20000'

Linux: UDP 20000

sudo ss -ulnp 'sport = :20000'

Linux / macOS: which process owns the port

sudo lsof -nP -i :20000

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':20000 '

Windows (Command Prompt)

netstat -ano | findstr :20000

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 20000 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 20000

From Windows

Test-NetConnection HOST -Port 20000

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 20000

ufw

sudo ufw deny 20000/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 20000 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 20000 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 20000' -Direction Inbound -Protocol TCP -LocalPort 20000 -Action Block

ufw

sudo ufw deny 20000/udp

iptables

sudo iptables -A INPUT -p udp --dport 20000 -j DROP

nftables

sudo nft add rule inet filter input udp dport 20000 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 20000' -Direction Inbound -Protocol UDP -LocalPort 20000 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.