The error message %Authorization failed is explicit. It indicates that the initial step, authentication (verifying the user's identity), was successful. However, the subsequent step, authorization (determining what the authenticated user is permitted to do), failed. This means the router (R1) successfully communicated with the TACACS+ server, but the server's policy for that user does not grant permission for the requested service, which is an EXEC shell session. The issue lies within the TACACS+ server's configuration, not with the router's configuration or network reachability. The resolution is to modify the user's profile or policy on the TACACS+ server to explicitly permit shell access.

A. The error is about authorization, not authentication. An authentication misconfiguration would typically result in a "login incorrect" message, not an authorization failure.

B. The specific error message confirms that the TACACS+ server is reachable and responded with a denial. If the server were unreachable, a timeout error would occur.

C. If the TACACS+ server host IP were not configured on R1, the router would not know where to send the AAA request, resulting in a different failure, not this specific message.

1. Cisco IOS Security Configuration Guide

Release 15M&T

"Implementing TACACS+": In the "Authorization Overview" section

it is stated

"Authorization is the process of granting or denying a user specific services or commands... Authorization is a separate function from authentication." This confirms that the failure is in a distinct step after successful authentication.

2. Cisco Identity Services Engine Administrator Guide

3.1

"Chapter: Device Administration": The section "Configure Policy Elements for Device Administration" details the configuration of "TACACS Profiles" and "Shell Profiles." It specifies that to grant EXEC shell access

a Shell Profile with appropriate privilege levels must be configured on the ISE (acting as the TACACS+ server) and applied to the user via a policy. An authorization failure occurs if no such policy matches or if the matching policy denies access.

3. Cisco IOS Security Command Reference

"aaa authorization": The documentation for the aaa authorization command explains that its purpose is to run authorization for a specific service (like exec for shell access) against the configured AAA server. The server's response dictates whether the user is granted access

and a denial from the server results in an authorization failure on the device.