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Port 4843 (opcua-tls)

IANA assigns port 4843 to opcua-tls: OPC UA TCP Protocol over TLS/SSL.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
opcua-tls TCP OPC UA TCP Protocol over TLS/SSL OPC Foundation -
opcua-tls UDP OPC UA TCP Protocol over TLS/SSL OPC Foundation -

Registry dates for this port: registered 2006-09, last modified 2017-05-23.

Check what is listening on port 4843

Linux: is anything listening on TCP 4843?
sudo ss -tlnp 'sport = :4843'
Linux: UDP 4843
sudo ss -ulnp 'sport = :4843'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4843
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4843 '
Windows (Command Prompt)
netstat -ano | findstr :4843
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4843 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4843
From Windows
Test-NetConnection HOST -Port 4843
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4843

Block port 4843 in the firewall

ufw
sudo ufw deny 4843/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4843 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4843 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4843' -Direction Inbound -Protocol TCP -LocalPort 4843 -Action Block
ufw
sudo ufw deny 4843/udp
iptables
sudo iptables -A INPUT -p udp --dport 4843 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4843 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4843' -Direction Inbound -Protocol UDP -LocalPort 4843 -Action Block

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