Server-based AAA (Authentication, Authorization, and Accounting) provides centralized management for network access control using dedicated protocols like TACACS+ and RADIUS. These protocols enable network administrators to manage user credentials and permissions from a single location rather than …Server-based AAA (Authentication, Authorization, and Accounting) provides centralized management for network access control using dedicated protocols like TACACS+ and RADIUS. These protocols enable network administrators to manage user credentials and permissions from a single location rather than configuring each device individually.
TACACS+ (Terminal Access Controller Access-Control System Plus) is a Cisco-proprietary protocol that uses TCP port 49 for reliable communication. It encrypts the entire packet payload, providing enhanced security for sensitive data transmission. TACACS+ separates authentication, authorization, and accounting into distinct processes, offering granular control over each function. This separation allows administrators to implement different servers for different AAA functions if needed.
RADIUS (Remote Authentication Dial-In User Service) is an open-standard protocol using UDP ports 1812 and 1813 (or legacy ports 1645 and 1646). Unlike TACACS+, RADIUS only encrypts the password field within packets, leaving other information visible. RADIUS combines authentication and authorization into a single process while keeping accounting separate. This protocol is widely supported across various vendor equipment.
Key differences between the two protocols include transport reliability, encryption scope, and protocol flexibility. TACACS+ offers more comprehensive security through full packet encryption and TCP-based delivery confirmation. RADIUS provides broader compatibility due to its open-standard nature and is commonly used for network access scenarios like VPN connections and wireless authentication.
Implementing server-based AAA involves configuring network devices as AAA clients that communicate with centralized servers. When users attempt access, the device forwards credentials to the AAA server for verification. The server responds with permission levels and logs all activities for audit purposes.
Organizations typically choose TACACS+ for device administration access due to its command-level authorization capabilities, while RADIUS remains popular for end-user network access authentication in enterprise environments.
Server-based AAA (Authentication, Authorization, and Accounting) is critical for enterprise network security because it provides centralized management of user access. Instead of configuring user credentials on each individual network device, administrators can manage all authentication from a single server. This approach enhances security, simplifies administration, reduces human error, and provides comprehensive audit trails for compliance requirements.
What is Server-based AAA?
Server-based AAA refers to the use of dedicated servers to handle the three security functions:
Authentication - Verifies user identity (who are you?) Authorization - Determines what the user can access (what can you do?) Accounting - Tracks user activities (what did you do?)
The two primary protocols used for server-based AAA are:
TACACS+ (Terminal Access Controller Access-Control System Plus) - Cisco proprietary protocol - Uses TCP port 49 - Encrypts the entire packet body - Separates authentication, authorization, and accounting into distinct functions - Best suited for device administration
RADIUS (Remote Authentication Dial-In User Service) - Open standard protocol - Uses UDP ports 1812 (authentication) and 1813 (accounting) - Encrypts only the password field - Combines authentication and authorization into a single process - Best suited for network access (VPN, wireless, 802.1X)
How Server-based AAA Works
1. A user attempts to access a network device or resource 2. The network device (AAA client) forwards the credentials to the AAA server 3. The AAA server checks its database or directory service 4. The server responds with an accept or reject message 5. If accepted, authorization parameters are applied 6. All activities are logged for accounting purposes
Key Differences Between TACACS+ and RADIUS
Transport Protocol: TACACS+ uses TCP; RADIUS uses UDP Encryption: TACACS+ encrypts entire payload; RADIUS encrypts password only AAA Functions: TACACS+ separates all three; RADIUS combines authentication and authorization Standard: TACACS+ is Cisco proprietary; RADIUS is an open standard Primary Use: TACACS+ for device administration; RADIUS for network access
Exam Tips: Answering Questions on Server-based AAA (TACACS+, RADIUS)
1. Remember the port numbers: TACACS+ uses TCP 49; RADIUS uses UDP 1812/1813. Questions often test this knowledge.
2. Focus on encryption differences: When a question asks about security or encryption, TACACS+ provides full packet encryption while RADIUS only protects the password.
3. Understand the separation of functions: TACACS+ allows granular control by separating AAA functions. Choose TACACS+ when questions mention granular authorization or device administration.
4. Consider the use case: Device administration scenarios point to TACACS+. Network access scenarios (wireless, VPN, 802.1X) point to RADIUS.
5. TCP vs UDP: If reliability or connection-oriented communication is mentioned, think TACACS+. If the question emphasizes broad compatibility or open standards, think RADIUS.
6. Cisco preference: For managing Cisco devices and command authorization, TACACS+ is the preferred choice due to its granular control capabilities.
7. Watch for keywords: Words like 'proprietary' or 'Cisco-developed' indicate TACACS+. Words like 'industry standard' or 'RFC-defined' indicate RADIUS.
8. Configuration questions: Know that AAA must be enabled first with aaa new-model before configuring server-based AAA.