Cisco TACACS+ and RADIUS: A Deep Dive into Network Access Control Protocols

In the realm of network security, controlling access to networks is paramount. Cisco, a leader in networking solutions, offers two prominent security protocols for this purpose: TACACS+ and RADIUS. This blog post aims to compare these protocols, providing insights into their functionalities and differences.

Background Information

RADIUS (Remote Authentication Dial-In User Service) and TACACS+ (Terminal Access Controller Access-Control System Plus) are protocols developed to secure remote access to networks and network services. Cisco supports both, acknowledging their importance in different scenarios.

RADIUS Background: Defined in RFC 2865, RADIUS is an access server protocol using AAA (Authentication, Authorization, and Accounting) architecture. It’s integral in securing remote network access through a distributed security system.

TACACS+ Development: Cisco developed TACACS+ after evaluating RADIUS, incorporating features to meet evolving security market demands. TACACS+ was designed to scale with network growth and adapt to new security technologies.

Key Features and Differences

UDP and TCP: RADIUS utilizes UDP (User Datagram Protocol), while TACACS+ uses TCP (Transmission Control Protocol). TCP’s connection-oriented nature provides advantages like reliable packet delivery and immediate server crash detection, making TACACS+ more scalable and adaptable to larger, congested networks.

Packet Encryption: A critical difference lies in their approach to encryption. RADIUS encrypts only the password in the access-request packet, leaving the rest of the packet unencrypted. In contrast, TACACS+ encrypts the entire packet body, offering enhanced security.

Authentication and Authorization: RADIUS combines authentication and authorization, sending both in the access-accept packets. TACACS+, with its AAA architecture, separates these functions. This separation allows for more flexible authentication solutions while using TACACS+ for authorization and accounting.

Multiprotocol Support and Router Management: TACACS+ supports a broader range of protocols than RADIUS and provides more control over router command authorization. This makes TACACS+ more versatile for complex network management tasks.

Usage Scenarios

RADIUS: Best suited for environments where remote user access to networks is the primary concern. It’s widely used for securing VPN, wireless, and Ethernet connections.

VPN Access Control:

    • RADIUS is extensively used for user authentication in VPN (Virtual Private Network) environments. It ensures that only authorized users can establish a VPN connection to the corporate network.

Wireless Network Security:

    • In wireless networking, RADIUS is employed for authenticating users before they access Wi-Fi networks. This is often seen in enterprise Wi-Fi setups where user credentials or certificates are required for network access.

Ethernet Network Access:

    • For wired networks, particularly those using 802.1X for port-based access control, RADIUS is used to authenticate devices connecting via Ethernet ports. This restricts network access to authorized devices only.

Dynamic VLAN Assignment:

    • RADIUS can dynamically assign VLANs (Virtual Local Area Networks) to users or devices as they log onto the network, allowing for segmenting network access based on user roles or device type.

Network Policy Enforcement:

    • RADIUS servers can enforce various network policies such as session timeout, idle timeout, and bandwidth restrictions, providing granular control over the network resources a user can access.

TACACS+: Ideal for detailed administrative control over network devices and scenarios requiring higher security and command-level authorization.

Network Device Administration:

    • TACACS+ is ideal for controlling access to network devices like routers, switches, and firewalls. It allows for managing who can log into these devices and what they can do after logging in.

Command Authorization:

    • With TACACS+, network administrators can control the specific commands users can execute on a device. This is crucial for preventing unauthorized changes to critical network configurations.

Role-Based Access Control:

    • TACACS+ supports role-based access control (RBAC) for network devices, allowing different levels of access and control for different user roles, such as network administrators, technicians, and auditors.

Detailed Auditing and Logging:

    • TACACS+ provides detailed logging of every command a user executes on a network device. This is vital for audit trails, security investigations, and compliance reporting.

Multi-Factor Authentication for Device Access:

    • TACACS+ can integrate with multi-factor authentication systems in environments requiring heightened security to ensure secure administrative access to network infrastructure.


Cisco’s support for RADIUS and TACACS+ highlights the diversity of network security needs. RADIUS is optimal for user-level network access control, while TACACS+ excels in device administration and command authorization. Understanding the strengths and applications of each protocol is crucial in making an informed choice for your network security strategy.

TACACS+ Security Perspective

 Full Packet Encryption

  • Entire Packet Encryption: Unlike RADIUS, which encrypts only the password portion of the packet, TACACS+ encrypts the entire body of the packet. This includes not only the authentication credentials but also the authorization and accounting data.
  • Reduced Vulnerability to Eavesdropping: This comprehensive encryption approach minimizes the risk of sensitive data being intercepted and decoded by unauthorized entities.

Separate Authentication, Authorization, and Accounting (AAA)

  • Modular Approach: TACACS+ handles authentication, authorization, and accounting as separate components. This separation allows for more flexibility and security. For instance, a user can be authenticated via one method (like using a password or certificate) and then authorized for specific commands or activities based on a different set of criteria.
  • Granular Control: This modularity enables more granular control over user actions. For example, after a user is authenticated, the system can precisely determine their authorization level, controlling which commands they can execute on the network device.

TCP-Based Communication

  • Reliable Packet Delivery: TACACS+ communicates with TCP (Transmission Control Protocol). TCP is a connection-oriented protocol that ensures reliable packet delivery. This means that the packets are guaranteed to reach their destination in the correct order and without loss, which is crucial for sensitive command and control communications.
  • Enhanced Server Availability Detection: TCP allows for immediate detection of a crashed or stopped server, as opposed to UDP (used by RADIUS), which cannot readily differentiate between a non-responsive and a slow server. This feature is vital for maintaining the integrity of network security.

Command-Level Authorization and Accounting

  • Detailed User Activity Tracking: TACACS+ can log every command executed by a user on a network device. This capability is crucial for auditing and compliance, providing a detailed activity trail.
  • Role-Based Access Control: It enables detailed role-based access control, where different users or groups can have different levels of access and permissions on network devices.

Extensibility and Adaptability

  • Scalability: TACACS+ is designed to be scalable, making it suitable for small and large networks.
  • Adaptable to New Security Measures: The protocol can adapt to new security technologies and requirements, making it a future-proof choice for evolving network environments.

Customization and Policy Implementation

  • Flexible Policy Implementation: TACACS+ allows for implementing complex and customized security policies tailored to specific organizational needs.
  • Vendor-Specific Extensions: TACACS+ can be extended with vendor-specific options, providing additional flexibility and control over authentication and authorization processes.


The security features of TACACS+ make it an ideal choice for network environments where security, particularly in device administration and access control, is a critical concern. Its ability to provide full packet encryption, separate AAA services, reliable TCP-based communication, detailed auditing, and customizable security policies collectively contribute to its reputation as a highly secure protocol.