A Brief Overview of RADIUS

RADIUS is also a protocol that supports the three portions of AAA. Cisco Systems introduced support for RADIUS in Cisco IOS Software Release 11.1. The RADIUS authentication protocol is documented separately from the accounting protocol; however, the two can be used together.

RADIUS was initially developed by Livingston Enterprises, Inc. RADIUS, covered in RFC 2865, is an open standard, as opposed to the TACACS+ protocol that is implemented by Cisco. RADIUS is an IP-based protocol that uses UDP, a client, and a server. The server returns a result on the information that is requested by a client. The information that the server returns to the client can be located on the RADIUS server or on an external device that the RADIUS server communicates with directly. When this is the case, the requesting client does not have any knowledge of this. Unlike TACACS+, RADIUS performs authentication and authorization at the same time and accounting separately.