The AAA (Authentication, Authorization, and Accounting) framework is used in network security to manage user access. In this framework, the Network Access Server (NAS) plays a specific role. In an HPE Aruba Networking environment, the NAS is typically a device like a Mobility Controller (MC) or an AOS-CX switch that interacts with an AAA server (e.g., ClearPass Policy Manager, CPPM) to authenticate users.
NAS Role in AAA:
Authentication: The NAS acts as a client to the AAA server (e.g., via RADIUS), forwarding authentication requests from the user’s device to the server. It does not perform the authentication itself; the AAA server authenticates the user.
Authorization: After authentication, the NAS receives authorization attributes from the AAA server (e.g., a user role via Aruba-User-Role VSA) and enforces access policies (e.g., firewall rules, VLAN assignment) based on those attributes.
Accounting: The NAS sends accounting information (e.g., session start/stop, data usage) to the AAA server to track user activity.
Option A, "It negotiates with each user’s device to determine which EAP method is used for authentication," is incorrect. The NAS does not negotiate the EAP method with the user’s device. The EAP method (e.g., EAP-TLS, PEAP) is determined by the configuration on the NAS and the AAA server, and the client must support the configured method. The negotiation of EAP methods occurs between the client (supplicant) and the AAA server, with the NAS acting as a pass-through.
Option B, "It determines which resources authenticated users are allowed to access and monitors each user’s session," is incorrect. The NAS enforces access policies based on authorization attributes received from the AAA server, but it does not determine which resources users can access—that decision is made by the AAA server based on its policies. Monitoring sessions is part of accounting, but this option overstates the NAS’s role in determining access.
Option C, "It enforces access to network services and sends accounting information to the AAA server," is correct. The NAS enforces access by applying policies (e.g., firewall rules, VLANs) based on the authorization attributes received from the AAA server. It also sends accounting information (e.g., session start/stop, data usage) to the AAA server to track user activity, fulfilling its role in the accounting part of AAA.
Option D, "It authenticates legitimate users and uses policies to determine which resources each user is allowed to access," is incorrect. The NAS does not authenticate users; the AAA server performs authentication. The NAS also does not determine resource access; it enforces the policies provided by the AAA server.
The HPE Aruba Networking AOS-8 8.11 User Guide states:
"In the AAA framework, the Network Access Server (NAS), such as a Mobility Controller, acts as a client to the AAA server (e.g., a RADIUS server). The NAS forwards authentication requests from the user’s device to the AAA server, enforces access to network services based on the authorization attributes returned by the server (e.g., user role, VLAN), and sends accounting information, such as session start and stop records, to the AAA server for tracking." (Page 310, AAA Framework Section)
Additionally, the HPE Aruba Networking ClearPass Policy Manager 6.11 User Guide notes:
"The NAS in the AAA framework, such as an Aruba Mobility Controller, does not authenticate users itself; it forwards authentication requests to the AAA server (ClearPass). After authentication, the NAS enforces access policies based on the server’s response and sends accounting data to the AAA server to log user activity, such as session duration and data usage." (Page 280, NAS Role in AAA Section)
[References:, HPE Aruba Networking AOS-8 8.11 User Guide, AAA Framework Section, Page 310., HPE Aruba Networking ClearPass Policy Manager 6.11 User Guide, NAS Role in AAA Section, Page 280.===========]
