What is Port 1812 used for?
Network authentication. The protocol or service commonly associated with this port is RADIUS Authentication.
Role and operation
An access device, known as a RADIUS client or NAS, normally sends an Access-Request to the server on UDP 1812. The server evaluates the available authentication information and can respond with Access-Accept, Access-Reject, or Access-Challenge. The shared secret protects selected parts of the exchange between the RADIUS client and server.
Transport protocol
UDP
Security precautions
Should this port be opened in the firewall?
Open UDP 1812 only from authorized access devices to the RADIUS server. An end-user Wi-Fi station normally does not contact this port directly when the access point or controller acts as the RADIUS client.
How can this port be checked?
Review logs on both the RADIUS server and NAS, then use an appropriate RADIUS test client when available. A packet capture can filter udp.port == 1812. Test-NetConnection -Port does not validate a UDP RADIUS service.
Port-to-service mappings are common conventions. An application may be configured on another port or use a different transport depending on its implementation.