In an Aruba User-Based Tunneling (UBT) environment, the switch relies on an authentication server (e.g., ClearPass) to provide the Aruba-User-Role attribute for an authenticated client. This attribute specifies the role to be applied by the gateway (Mobility Controller). If the authentication server successfully authenticates a client but fails to return this specific gateway role, the switch cannot establish the tunnel for that client. The switch's default fallback behavior in this scenario is to place the client on the port's configured access VLAN and forward its traffic locally, as if it were a standard, non-tunneled client.

B. The gateway will assign a default role to the client.

This is incorrect because the premise is that the gateway did not receive a role; therefore, it cannot take any action, including assigning a default one.

C. The switch will assign the default deny role to the client.

This is incorrect. The switch's default action is to revert to local forwarding on the access VLAN, not to apply a specific named "deny role".

D. The gateway will send back the deny role to the client.

This is incorrect as it contradicts the question's scenario where the gateway does not specify any role for the client.

1. ArubaOS-Switch Advanced Traffic Management Guide K.16.03

Chapter 7: "Per-User Tunneled Node"

Page 161

"Operation notes": "If the authentication server does not return a gateway role for an authenticated client

the switch places the client in the access VLAN and forwards its traffic locally."

2. ArubaOS-Switch Access Security Guide for 16.10

Chapter 11: "Tunneled Node"

Page 301

"RADIUS attributes for tunneled node": This section details the necessity of the Aruba-User-Role Vendor-Specific Attribute (VSA) for the gateway to assign a policy. Its absence leads to the failure condition described in the question.