TACACS+

TACACS+ (Terminal Access Controller Access-Control System Plus) is an AAA protocol created by Cisco. It helps manage secure access to network devices like routers, switches, and firewalls. While it was initially proprietary, TACACS+ is now widely supported by other vendors, making it a great choice for complex networks.

Purpose of TACACS+

TACACS+ is designed for detailed access control. Unlike other protocols, it separates the three AAA functions, which are Authentication, Authorization and Accounting to give administrators more control over user access, actions, and logs.

How TACACS+ Works

TACACS+ uses a client-server model with TCP on port 49 to ensure reliable and secure communication. Here’s how it works:

• TACACS+ Client: The network device (example a router or switch) sends user login details to the TACACS+ server for verification.

• TACACS+ Server: This is the central system that verifies user credentials, checks permissions, and logs all user actions.

Unlike RADIUS, TACACS+ encrypts all the data sent between the client and server, making it more secure for sensitive networks.

In TACACS+, the authentication process is fully encrypted, which protects all user details during transmission.

Authentication Workflow

Here’s how TACACS+ authenticates a user:

1. Authentication Request: The network device (client) sends the user’s login details to the TACACS+ server.

2. Server Response: The server checks the credentials and replies with either:

   • Accept: The user is granted access.

   • Reject: Access is denied if the credentials are incorrect.

This encryption ensures no sensitive data is exposed, even if someone intercepts the communication.

Authorization

TACACS+ provides granular control over user actions:

• Command-Level Authorization: Every command a user tries to execute is checked against their permissions.

• Example: A user might be allowed to run show run to view the configuration but not use configure terminal to make changes.

This ensures users can only perform tasks they are authorized for, improving both security and accountability.

Accounting

TACACS+ keeps detailed logs of all user actions:

• Command Logging: Every command a user executes is recorded.

• Session Details: Tracks when users log in, log out, and the results of their actions.

These logs create a full audit trail, making it easier to troubleshoot issues or review compliance.

Setting up TACACS+ on a Cisco device involves defining the TACACS+ server, enabling AAA, and applying the configuration to user authentication. Here’s a step-by-step guide: