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Port 8503 (lsp-self-ping)

IANA assigns port 8503 to lsp-self-ping: MPLS LSP Self-Ping.

Registered (user) port, 1024-49151 UDP

Port 8503 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
lsp-self-ping UDP MPLS LSP Self-Ping IESG RFC 7746

Registry dates for this port: registered 2015-06-11, last modified 2016-02-01.

Check what is listening on port 8503

Linux: UDP 8503
sudo ss -ulnp 'sport = :8503'
Linux / macOS: which process owns the port
sudo lsof -nP -i :8503
Windows (Command Prompt)
netstat -ano | findstr :8503
Windows (PowerShell)
Get-NetUDPEndpoint -LocalPort 8503

Test it from outside

UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 8503

Block port 8503 in the firewall

ufw
sudo ufw deny 8503/udp
iptables
sudo iptables -A INPUT -p udp --dport 8503 -j DROP
nftables
sudo nft add rule inet filter input udp dport 8503 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 8503' -Direction Inbound -Protocol UDP -LocalPort 8503 -Action Block

Related ports

8501cmtp-mgt, cmtp-av8502ftnmtp8554RTSP alternate8555d-fence

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