Port 6817 (pentbox-sim)

IANA assigns port 6817 to pentbox-sim: PenTBox Secure IM Protocol.

Registered (user) port, 1024-49151 TCP

IANA assignment

Service nameProtoDescriptionAssigneeReference

pentbox-sim TCP PenTBox Secure IM Protocol Alberto Ortega Llama -

Registry dates for this port: registered 2009-11-04.

Linux: is anything listening on TCP 6817?

sudo ss -tlnp 'sport = :6817'

Linux / macOS: which process owns the port

sudo lsof -nP -i :6817

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':6817 '

Windows (Command Prompt)

netstat -ano | findstr :6817

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 6817 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 6817

From Windows

Test-NetConnection HOST -Port 6817

ufw

sudo ufw deny 6817/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 6817 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 6817 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 6817' -Direction Inbound -Protocol TCP -LocalPort 6817 -Action Block

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