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Port 4191 (dsmipv6)

IANA assigns port 4191 to dsmipv6: Dual Stack MIPv6 NAT Traversal.

Registered (user) port, 1024-49151 UDP

Port 4191 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
dsmipv6 UDP Dual Stack MIPv6 NAT Traversal - RFC 5555

Check what is listening on port 4191

Linux: UDP 4191
sudo ss -ulnp 'sport = :4191'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4191
Windows (Command Prompt)
netstat -ano | findstr :4191
Windows (PowerShell)
Get-NetUDPEndpoint -LocalPort 4191

Test it from outside

UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4191

Block port 4191 in the firewall

ufw
sudo ufw deny 4191/udp
iptables
sudo iptables -A INPUT -p udp --dport 4191 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4191 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4191' -Direction Inbound -Protocol UDP -LocalPort 4191 -Action Block

Related ports

4189pcep4190sieve4192azeti, azeti-bd4193pvxplusio

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