Certified - CompTIA Network +

In Episode One Hundred Forty-Four we take a deep dive into how large-scale network environments manage access consistently across multiple systems and devices. In smaller setups, user accounts might be configured locally on each device. But in enterprise environments, this approach becomes inefficient, inconsistent, and insecure. Centralized authentication addresses this problem by providing a single location where access control policies, credentials, and permissions can be managed. For Network Plus candidates, these systems are often referenced in access control and identity management exam questions.
The purpose of centralized authentication is to simplify user management while ensuring consistent enforcement of policies. Instead of managing users individually across switches, routers, firewalls, and servers, centralized authentication allows administrators to define user credentials, roles, and permissions once, and apply them across the infrastructure. This enables rapid onboarding and offboarding, simplifies auditing, and strengthens overall security. This episode will cover how protocols like RADIUS and T A C A C S Plus, as well as directory services and Single Sign-On, come together to support centralized access control. You’ll need to understand these mechanisms both for the exam and for real-world deployment.
At its core, centralized authentication is about creating one place to manage user identities. Instead of manually creating usernames and passwords on every switch or firewall, devices are configured to consult an external authentication server—usually integrated with a directory service like Active Directory or LDAP. The user logs into the network device, the device forwards the credentials to the authentication server, and access is granted or denied based on centrally stored policies. This greatly reduces the configuration burden and ensures that all users are held to the same standards. On the exam, you’ll often see scenarios that describe centralized authentication workflows and ask you to identify the components.
There are several benefits to this centralized control. First, it makes user management easier—adding, removing, or updating users only has to happen once. Second, it supports better auditing and accountability. Because login attempts are recorded at a central location, you always know who accessed what and when. Third, it ensures consistent policy enforcement. You don’t have to worry about mismatched password requirements or outdated user accounts on isolated devices. On the Network Plus exam, expect to identify these advantages in questions that compare local and centralized access methods.
RADIUS stands for Remote Authentication Dial-In User Service. Despite its name, it is widely used far beyond dial-in access. RADIUS is a UDP-based protocol that provides centralized authentication, authorization, and accounting—commonly referred to as AAA. When a user attempts to access a device or network resource, their credentials are sent to the RADIUS server, which checks them against a central database. RADIUS is commonly used in wireless networks, VPNs, and remote access systems. On the exam, you'll need to recognize RADIUS as a key protocol for centralized network access control.
RADIUS supports a variety of access types, including remote login, Wi-Fi authentication, and VPN connections. It centralizes user credentials, allowing administrators to apply consistent password policies and access restrictions. One of its key features is built-in accounting—RADIUS logs connection attempts, durations, and resource usage, which is valuable for auditing and troubleshooting. While it doesn’t encrypt the entire payload, it does obfuscate passwords. Expect to see RADIUS used in exam scenarios involving multi-user access to wireless or remote services.
TACACS Plus, or Terminal Access Controller Access-Control System Plus, is a Cisco-developed protocol that also supports centralized AAA services. Unlike RADIUS, TACACS Plus uses TCP instead of UDP and encrypts the entire communication payload, not just the password field. This makes it particularly well-suited for administrative access to network devices. Another key difference is that TACACS Plus separates authentication, authorization, and accounting into distinct functions, offering more granular control over what commands a user is allowed to execute. On the exam, expect to be tested on the distinctions between RADIUS and TACACS Plus.
TACACS Plus is ideal for environments where command-level authorization is needed. For example, one administrator might be allowed to view configuration settings but not change them. Another might have full privileges. This level of detail is difficult to enforce using RADIUS alone. TACACS Plus also supports robust logging, which helps administrators track which commands were issued and by whom. This level of visibility is useful for both security and compliance. On the exam, be prepared to choose TACACS Plus for use cases involving administrative control over network hardware.
Comparing RADIUS and TACACS Plus is a common task on the Network Plus exam. RADIUS is better suited for general network access—like authenticating wireless users or VPN sessions—because it’s lightweight and designed for speed. TACACS Plus, on the other hand, is better suited for administrative access to infrastructure devices due to its command-level control and full payload encryption. Both protocols support AAA, but their roles and applications differ. You may be asked to identify which protocol is appropriate based on a scenario’s requirements for security, functionality, and access type.
Single Sign-On, or SSO, is another element of centralized authentication. With SSO, users log in once and gain access to multiple systems or services without needing to re-enter credentials for each one. This reduces user fatigue, improves efficiency, and simplifies credential management. SSO is especially useful in environments with dozens of internal applications, cloud services, and portals. However, because SSO centralizes access, a compromise of the SSO system can provide an attacker with broad access. That’s why SSO should always be paired with strong authentication and session management controls. On the exam, you’ll be expected to recognize SSO’s benefits and its limitations.
SSO does make the login process more convenient, but it also introduces new risks. If a user’s SSO credentials are stolen, every connected service could be accessed. This is why it’s critical to pair SSO with multifactor authentication, strong password policies, and session timeouts. Secure tokens and encrypted sessions should be enforced. Session hijacking and cookie theft are among the common risks SSO must mitigate. For the exam, understand that while SSO reduces complexity, it also requires stronger protections to maintain overall security posture.
For more cyber-related content and books, please check out cyber author dot me. Also, there are other podcasts on Cybersecurity and more at Bare Metal Cyber dot com.
Directory services are at the heart of centralized authentication. These systems store user, group, and device information in a structured format and are accessed by authentication protocols like RADIUS, TACACS+, or LDAP. Directory services allow organizations to define access rules, assign group policies, and manage permissions from a central location. The most common examples are Microsoft Active Directory and the open-standard Lightweight Directory Access Protocol, or LDAP. On the exam, expect questions about directory structure, function, and how these systems integrate with authentication tools across a network.
Active Directory, or A D, is the dominant directory service in enterprise Windows environments. It manages domain resources, enforces security policies through Group Policy Objects, and integrates tightly with Windows-based authentication. A D supports centralized login, access control, and user management. When integrated with authentication protocols like RADIUS or TACACS+, it enables seamless role-based access and permission enforcement. On the exam, anticipate scenarios where Active Directory is used to manage domain-based access and enforce security through policy objects and centralized control.
LDAP, or Lightweight Directory Access Protocol, is another standard directory service used across many platforms, including Linux, UNIX, and hybrid environments. Unlike Active Directory, which is deeply tied to Windows, LDAP is platform-agnostic and more flexible in environments with varied operating systems. LDAP allows administrators to query directory entries and authenticate users without managing local credentials on each device. It’s often used in applications like VPN authentication, Wi-Fi access, and internal portals. The exam may test your ability to distinguish between LDAP and Active Directory and recognize use cases for each.
Network devices such as firewalls, switches, and routers can be integrated with directory services to use centralized authentication rather than local accounts. This allows consistent enforcement of access rules across the environment. For instance, a switch can be configured to allow only users in the “NetworkOps” group to access configuration settings. Firewall administrative portals can require authentication against a centralized identity store. This reduces the sprawl of unmanaged accounts and simplifies auditing. On the exam, you may be asked how device integration with directories supports better access management.
Logging and auditing are critical features of centralized authentication. Every login attempt—successful or failed—is logged, and these logs are stored centrally for analysis. Audit trails help identify who accessed what, when, and from where. If unauthorized access is attempted or credentials are compromised, these logs provide crucial forensic evidence. They also help meet regulatory requirements and support internal investigations. The exam may include questions about the purpose of centralized logging and the importance of authentication audit trails in maintaining accountability.
Redundancy and failover are essential to maintaining uptime in authentication systems. If the central authentication server fails and no backup is available, users may be locked out of critical systems. To prevent this, organizations deploy multiple authentication servers, often load-balanced or configured in a primary-secondary model. In some cases, devices can fall back to local authentication if the directory is unreachable. These configurations ensure that access control continues even if part of the system fails. Expect exam questions that involve designing resilient authentication architectures and recognizing where local fallbacks are appropriate.
The Network Plus exam regularly includes topics related to centralized authentication. You’ll need to know the differences between TACACS+ and RADIUS, including their transport protocols, encryption methods, and usage contexts. You’ll be asked to identify which services are best suited for administrative access versus network access. You’ll also need to recognize common directory service terms, understand integration workflows, and match authentication models to network roles. Questions may combine authentication with security policy enforcement or device configuration management.
To summarize, centralized identity models provide a scalable, secure, and manageable way to control access across the network. By consolidating user authentication through RADIUS, TACACS+, SSO, and directory services like Active Directory or LDAP, organizations can reduce administrative burden, improve visibility, and enforce consistent policies. These systems support accountability, enable rapid provisioning and deprovisioning, and make security audits more efficient. Understanding how each component works—and how they fit together—is essential for both passing the exam and managing real-world network environments effectively.
To conclude Episode One Hundred Forty-Four, remember that centralized authentication is the backbone of access control in today’s networks. TACACS+ and RADIUS allow centralized login enforcement and policy control. Single Sign-On simplifies access for users, while directory services provide the structure to support it all. Together, these systems enable secure, streamlined management across diverse environments. Whether you’re securing infrastructure, supporting compliance, or preparing for the Network Plus exam, mastering these authentication tools will be a key part of your success.