Port 3389 — TCP/UDP
Microsoft Remote Desktop connections.
What is port 3389 used for?
Remote desktop access; UDP can supplement TCP depending on the configuration.
Transport protocol
TCP/UDP
Security precautions
Avoid direct Internet exposure. Use a VPN or RD Gateway, MFA and Network Level Authentication where supported.
Should we open this port in the firewall?
Allow this port only when a required service uses it. Apply least privilege: restrict authorized sources, destinations and interfaces, and log connections where appropriate.
How do I check this port?
Test-NetConnection SERVER -Port 3389Test-NetConnection SERVER -Port 3389 and nc -vz SERVER 3389 check TCP only. If the service uses UDP, reproduce a real application exchange and inspect logs or a packet capture for UDP 3389; a TCP success does not validate UDP.
Port-to-service mappings are common conventions. Applications can use a different configured port; confirm the actual service and transport.