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Port 4747 (buschtrommel)

IANA assigns port 4747 to buschtrommel: peer-to-peer file exchange protocol.

Registered (user) port, 1024-49151 UDP

Port 4747 is normally used over UDP; the checker tests TCP only, so a "filtered" result does not mean the UDP service is down.

IANA assignment

Service nameProtoDescriptionAssigneeReference
buschtrommel UDP peer-to-peer file exchange protocol Tobias Sturm -

Registry dates for this port: registered 2013-01-14.

Check what is listening on port 4747

Linux: UDP 4747
sudo ss -ulnp 'sport = :4747'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4747
Windows (Command Prompt)
netstat -ano | findstr :4747
Windows (PowerShell)
Get-NetUDPEndpoint -LocalPort 4747

Test it from outside

UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4747

Block port 4747 in the firewall

ufw
sudo ufw deny 4747/udp
iptables
sudo iptables -A INPUT -p udp --dport 4747 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4747 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4747' -Direction Inbound -Protocol UDP -LocalPort 4747 -Action Block

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