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Port 1983 (lhtp)

IANA assigns port 1983 to lhtp: Loophole Test Protocol.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
lhtp TCP Loophole Test Protocol Kade Hansson -
lhtp UDP Loophole Test Protocol Kade Hansson -

Check what is listening on port 1983

Linux: is anything listening on TCP 1983?
sudo ss -tlnp 'sport = :1983'
Linux: UDP 1983
sudo ss -ulnp 'sport = :1983'
Linux / macOS: which process owns the port
sudo lsof -nP -i :1983
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':1983 '
Windows (Command Prompt)
netstat -ano | findstr :1983
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 1983 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 1983
From Windows
Test-NetConnection HOST -Port 1983
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 1983

Block port 1983 in the firewall

ufw
sudo ufw deny 1983/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 1983 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 1983 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 1983' -Direction Inbound -Protocol TCP -LocalPort 1983 -Action Block
ufw
sudo ufw deny 1983/udp
iptables
sudo iptables -A INPUT -p udp --dport 1983 -j DROP
nftables
sudo nft add rule inet filter input udp dport 1983 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 1983' -Direction Inbound -Protocol UDP -LocalPort 1983 -Action Block

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