Correct Answer: A
Explanation: RADIUS is an access server that uses AAA protocol. It is a system of distributed security that secures remote access to networks and network services against unauthorized access. RADIUS comprises three components:
* A protocol with a frame format that utilizes User Datagram Protocol (UDP)/IP.
* A server.
* A client.
The server runs on a central computer typically at the customer's site, while the clients reside in the dial-up access servers and can be distributed throughout the network. Cisco has incorporated the RADIUS Client into Cisco IOS Software Release 11.1 and later and other device software.
Client/Server Model
A network access server (NAS) operates as a client of RADIUS. The client is responsible for passing user information to designated RADIUS servers, and then acting on the response that is returned. RADIUS servers are responsible for receiving user connection requests, authenticating the user, and returning all configuration information necessary for the client to deliver service to the user. The RADIUS servers can act as proxy clients to other kinds of authentication servers.
Network Security
Transactions between the client and RADIUS server are authenticated through the use of a shared secret, which is never sent over the network. In addition, any user passwords are sent encrypted between the client and RADIUS server. This eliminates the possibility that someone snooping on an unsecured network could determine a user's password.
Flexible Authentication Mechanisms
The RADIUS server supports a variety of methods to authenticate a user. When it is provided with the user name and original password given by the user, it can support PPP, Password Authentication Protocol (PAP), or Challenge Handshake Authentication Protocol (CHAP), UNIX login, and other authentication mechanisms.
RADIUS does not support these protocols:
* AppleTalk Remote Access (ARA) protocol
* NetBIOS Frame Protocol Control protocol
* Novell Asynchronous Services Interface (NASI)
* X.25 PAD connection
TACACS+ offers multiprotocol support.