HTTPfy

Port 1823 (unisys-lm)

IANA assigns port 1823 to unisys-lm: Unisys Natural Language License Manager.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
unisys-lm TCP Unisys Natural Language License Manager Raymond A Diedrichs -
unisys-lm UDP Unisys Natural Language License Manager Raymond A Diedrichs -

Check what is listening on port 1823

Linux: is anything listening on TCP 1823?
sudo ss -tlnp 'sport = :1823'
Linux: UDP 1823
sudo ss -ulnp 'sport = :1823'
Linux / macOS: which process owns the port
sudo lsof -nP -i :1823
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':1823 '
Windows (Command Prompt)
netstat -ano | findstr :1823
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 1823 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 1823
From Windows
Test-NetConnection HOST -Port 1823
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 1823

Block port 1823 in the firewall

ufw
sudo ufw deny 1823/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 1823 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 1823 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 1823' -Direction Inbound -Protocol TCP -LocalPort 1823 -Action Block
ufw
sudo ufw deny 1823/udp
iptables
sudo iptables -A INPUT -p udp --dport 1823 -j DROP
nftables
sudo nft add rule inet filter input udp dport 1823 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 1823' -Direction Inbound -Protocol UDP -LocalPort 1823 -Action Block

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