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Port 6636 (mpls-udp-dtls)

IANA assigns port 6636 to mpls-udp-dtls: Encapsulate MPLS packets in UDP tunnels with DTLS..

Registered (user) port, 1024-49151 UDP

Port 6636 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
mpls-udp-dtls UDP Encapsulate MPLS packets in UDP tunnels with DTLS. IESG RFC 7510

Registry dates for this port: registered 2015-02-10.

Check what is listening on port 6636

Linux: UDP 6636
sudo ss -ulnp 'sport = :6636'
Linux / macOS: which process owns the port
sudo lsof -nP -i :6636
Windows (Command Prompt)
netstat -ano | findstr :6636
Windows (PowerShell)
Get-NetUDPEndpoint -LocalPort 6636

Test it from outside

UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 6636

Block port 6636 in the firewall

ufw
sudo ufw deny 6636/udp
iptables
sudo iptables -A INPUT -p udp --dport 6636 -j DROP
nftables
sudo nft add rule inet filter input udp dport 6636 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 6636' -Direction Inbound -Protocol UDP -LocalPort 6636 -Action Block

Related ports

6634mpls-pm6635mpls-udp6640ovsdb6653openflow

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