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Port 4840 (opcua-tcp, opcua-udp)

IANA assigns port 4840 to opcua-tcp, opcua-udp: OPC UA Connection Protocol.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
opcua-tcp TCP OPC UA Connection Protocol OPC Foundation -
opcua-udp UDP OPC UA Multicast Datagram Protocol OPC Foundation -

Registry dates for this port: registered 2006-09, last modified 2018-01-04.

Check what is listening on port 4840

Linux: is anything listening on TCP 4840?
sudo ss -tlnp 'sport = :4840'
Linux: UDP 4840
sudo ss -ulnp 'sport = :4840'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4840
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4840 '
Windows (Command Prompt)
netstat -ano | findstr :4840
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4840 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4840
From Windows
Test-NetConnection HOST -Port 4840
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4840

Block port 4840 in the firewall

ufw
sudo ufw deny 4840/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4840 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4840 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4840' -Direction Inbound -Protocol TCP -LocalPort 4840 -Action Block
ufw
sudo ufw deny 4840/udp
iptables
sudo iptables -A INPUT -p udp --dport 4840 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4840 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4840' -Direction Inbound -Protocol UDP -LocalPort 4840 -Action Block

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All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.