HTTPfy

Port 3747 (linktest-s)

IANA assigns port 3747 to linktest-s: LXPRO.COM LinkTest SSL.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
linktest-s TCP LXPRO.COM LinkTest SSL Greg Bailey -
linktest-s UDP LXPRO.COM LinkTest SSL Greg Bailey -

Registry dates for this port: registered 2003-04.

Check what is listening on port 3747

Linux: is anything listening on TCP 3747?
sudo ss -tlnp 'sport = :3747'
Linux: UDP 3747
sudo ss -ulnp 'sport = :3747'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3747
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3747 '
Windows (Command Prompt)
netstat -ano | findstr :3747
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3747 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3747
From Windows
Test-NetConnection HOST -Port 3747
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3747

Block port 3747 in the firewall

ufw
sudo ufw deny 3747/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3747 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3747 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3747' -Direction Inbound -Protocol TCP -LocalPort 3747 -Action Block
ufw
sudo ufw deny 3747/udp
iptables
sudo iptables -A INPUT -p udp --dport 3747 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3747 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3747' -Direction Inbound -Protocol UDP -LocalPort 3747 -Action Block

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3745gw-call-port3746linktest3748webdata3749cimtrak

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