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Port 503 (intrinsa)

IANA assigns port 503 to intrinsa: Intrinsa.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
intrinsa TCP Intrinsa Robert Ford -
intrinsa UDP Intrinsa Robert Ford -

Check what is listening on port 503

Linux: is anything listening on TCP 503?
sudo ss -tlnp 'sport = :503'
Linux: UDP 503
sudo ss -ulnp 'sport = :503'
Linux / macOS: which process owns the port
sudo lsof -nP -i :503
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':503 '
Windows (Command Prompt)
netstat -ano | findstr :503
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 503 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 503
From Windows
Test-NetConnection HOST -Port 503
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 503

Block port 503 in the firewall

ufw
sudo ufw deny 503/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 503 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 503 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 503' -Direction Inbound -Protocol TCP -LocalPort 503 -Action Block
ufw
sudo ufw deny 503/udp
iptables
sudo iptables -A INPUT -p udp --dport 503 -j DROP
nftables
sudo nft add rule inet filter input udp dport 503 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 503' -Direction Inbound -Protocol UDP -LocalPort 503 -Action Block

Related ports

501stmf502Modbus/TCP504citadel505mailbox-lm

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