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Port 6696 (babel)

IANA assigns port 6696 to babel: Babel Routing Protocol.

Registered (user) port, 1024-49151 UDP

Port 6696 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
babel UDP Babel Routing Protocol - RFC 8966

Registry dates for this port: last modified 2011-08-15.

Check what is listening on port 6696

Linux: UDP 6696
sudo ss -ulnp 'sport = :6696'
Linux / macOS: which process owns the port
sudo lsof -nP -i :6696
Windows (Command Prompt)
netstat -ano | findstr :6696
Windows (PowerShell)
Get-NetUDPEndpoint -LocalPort 6696

Test it from outside

UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 6696

Block port 6696 in the firewall

ufw
sudo ufw deny 6696/udp
iptables
sudo iptables -A INPUT -p udp --dport 6696 -j DROP
nftables
sudo nft add rule inet filter input udp dport 6696 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 6696' -Direction Inbound -Protocol UDP -LocalPort 6696 -Action Block

Related ports

6689tsa6690cleverdetect6697IRC over TLS6699babel-dtls

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