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Port 11751 (intrepid-ssl)

IANA assigns port 11751 to intrepid-ssl: Intrepid SSL.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
intrepid-ssl TCP Intrepid SSL Robert Eden -
intrepid-ssl UDP Intrepid SSL Robert Eden -

Registry dates for this port: registered 2003-03.

Check what is listening on port 11751

Linux: is anything listening on TCP 11751?
sudo ss -tlnp 'sport = :11751'
Linux: UDP 11751
sudo ss -ulnp 'sport = :11751'
Linux / macOS: which process owns the port
sudo lsof -nP -i :11751
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':11751 '
Windows (Command Prompt)
netstat -ano | findstr :11751
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 11751 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 11751
From Windows
Test-NetConnection HOST -Port 11751
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 11751

Block port 11751 in the firewall

ufw
sudo ufw deny 11751/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 11751 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 11751 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 11751' -Direction Inbound -Protocol TCP -LocalPort 11751 -Action Block
ufw
sudo ufw deny 11751/udp
iptables
sudo iptables -A INPUT -p udp --dport 11751 -j DROP
nftables
sudo nft add rule inet filter input udp dport 11751 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 11751' -Direction Inbound -Protocol UDP -LocalPort 11751 -Action Block

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