What is the RADIUS default authentication port number?

RADIUS, which stands for Remote Authentication Dial-In User Service, primarily uses the User Datagram Protocol (UDP) for transport, and its default authentication port number is 1812. This port is specifically designated for RADIUS authentication requests, allowing clients to securely transmit user credentials to a RADIUS server for validation.

In practical terms, knowing this default port is essential for network administrators configuring RADIUS on firewalls, VPNs, and various network devices. If the ports are incorrectly set, or if a network security policy restricts traffic on port 1812, it can lead to authentication failures or bottlenecks.

The other options represent standard port numbers for different services. Port 80 is associated with HTTP traffic, port 443 is used for HTTPS, and port 22 is designated for SSH connections. Understanding these ports helps clarify RADIUS's distinct role in network authentication compared to other protocols and services.