How to Choose the Right Network Access Control (NAC) for Your Organization

Network Access Control, or NAC, is a technology many people have heard of, and some may have already tested in their own environments. However, a common issue today is that “NAC cannot be used effectively in real-world deployment” due to factors such as system slowness, inconsistent network control, or successful PoC results that fail in actual implementation. Let’s take a deeper look at why NAC can encounter these problems and how to select the right NAC solution for your organization.

The Role of NAC The role of NAC is quite straightforward—it controls access to the network. To enforce access control, NAC devices must first identify and classify all devices within the network, such as PCs, servers, printers, IP phones, switches, routers, and access points. Afterward, policies can be applied based on security requirements, including authentication, access rights to servers and printers, protocol usage permissions, and even enforcement of software installation and patching.

Overall, NAC functions can be categorized as follows:

Automatic Discovery and Classification: Once NAC is deployed, it should automatically discover all devices in the network and present a comprehensive overview. It then classifies devices based on OS types or network roles. In some cases, organizations deploy NAC primarily for discovery purposes due to device diversity, BYOD usage, or legacy systems. Solutions that provide vendor-agnostic visibility across the network are highly sought after.

Identity-based Policy Enforcement: NAC can enforce security policies based on user or device identity. It determines access rights based on authentication methods such as MAC authentication, 802.1X, or web authentication, and integrates with identity sources like Microsoft AD, LDAP, RADIUS, or local databases. Organizations can also define policies based on departments or user roles. Guest users may register through a portal and receive temporary access. Network-based Policy Enforcement: NAC can enforce network-level access control per user, similar to deploying a firewall at each endpoint. The method of enforcement varies by vendor—such as agent-based, SNMP, switch/firewall control, 802.1X, virtual firewall, or even ARP spoofing in extreme cases. Application-based Policy Enforcement: NAC can control application usage by enforcing installation of required software (e.g., antivirus, patch updates) and restricting unauthorized applications. This is done via agent software or remote control through administrative privileges. IPS-based Policy Enforcement: NAC can function as an intrusion prevention system (IPS), detecting suspicious activities such as network scanning, abnormal port access, or unusual traffic behavior, and restricting access accordingly. Real-Time Monitoring and Reporting: A good NAC solution should provide real-time monitoring dashboards and detailed reporting for analysis and incident response. However, not all NAC solutions offer these capabilities. Therefore, organizations should evaluate multiple vendors before making a decision. NAC Architecture: Inline vs. Out-of-Band NAC deployment architectures can generally be divided into two types: Inline NAC: Installed directly in the data path, similar to a firewall or IPS. While effective, it may introduce latency or cause network downtime if the device fails, unless redundancy is implemented—which increases cost and complexity. Out-of-Band NAC: Deployed outside the data path, allowing the network to operate at normal speed while enforcing access control. However, different vendors use different technologies, each with its own strengths and weaknesses. Out-of-Band Technology: Pros and Cons Common Out-of-Band NAC methods include: Virtual Firewall: Creates a virtual firewall without modifying network configurations or installing agents. Pros: Simple, efficient, minimal network impact Cons: Available only in certain solutions 802.1X: Standard-based authentication at the switch port level. Pros: Highly secure Cons: Complex deployment, requires full infrastructure support and endpoint configuration Stateful DHCP: Uses DHCP monitoring to assign access levels. Pros: Easy to deploy Cons: Vulnerable to IP spoofing or static IP usage Switch/Firewall Control: Uses SNMP or proprietary protocols to modify ACLs dynamically. Pros: Works well within the same vendor ecosystem Cons: Can impact performance and complicate network management Agent Control: Uses endpoint agents to enforce policies. Pros: Minimal network impact Cons: Not suitable for legacy systems or guest users ARP Spoofing: Intercepts traffic to enforce control. Pros: Easy to deploy Cons: Introduces security risks and network overhead ForeScout CounterACT: The Right NAC for You ForeScout is a leading Out-of-Band NAC solution offering multiple enforcement methods, including virtual firewall, 802.1X, switch/firewall control, and agent-based control. It supports identity-based, network-based, and application-based policies, along with advanced device discovery and classification down to firmware level. In Thailand, ForeScout CounterACT has been successfully deployed in large organizations with over 9,000 to 20,000 users. Reference sites are crucial when evaluating NAC solutions, as NAC impacts a wide range of users. User acceptance and experienced implementation teams are key success factors. For more information: https://www.throughwave.co.th/products/forescout-technologies/