You can knock, but you can’t get in

There is a new form of network control called Network Access Control (NAC) that will have a major impact on industrial Ethernet networks. NAC has been in the IT press for several years, but it has only recently starting to hit mainstream IT organizations. NAC is the general name given for systems that manage device access to wireless and wired networks.


There is a new form of network control called Network Access Control (NAC) that will have a major impact on industrial Ethernet networks. NAC has been in the IT press for several years, but it has only recently starting to hit mainstream IT organizations.

NAC is the general name given for systems that manage device access to wireless and wired networks. It handles user authentication and user permissions, as well as antivirus, antispyware, application, and O/S patch and upgrade status checking.

NAC has been widely used at universities and colleges that have private networks but operate in a public environment. A typical NAC implementation will allow network access only to devices that are registered, where there is a valid user account and where all required patches have been installed. The NAC improves network security by ensuring that all endpoint devices comply with corporate IT security policies prior to allowing access to the corporate network or to an approved virtual LAN (VLAN). If a device does not meet policy requirements, it is usually directed to a special VLAN with restricted access.

Emerging standards

There are a number of established and emerging standards for NAC systems that have made them easier to install and manage, including IEEE 802.1X, Extensible Authentication Protocol (EAP), Remote Authentication Dial-In User Service (RADIUS), and the efforts of the Trusted Computing Group (TGC, with information found at ). The TGC members develop and support open, vendor-neutral, industry standard specifications for trusted computing building blocks and software interfaces across multiple platforms. The existence of these standards means there is a good chance your company will use NAC in the future.

NAC will have an impact on networks based on industrial Ethernet because of NAC’s automatic checking of security and patch policies prior to network access. Industrial endpoint devices—such as embedded PCs, HMI stations, and dedicated application servers—will have different antivirus, antispyware, application, and O/S patch policies than standard office environment systems.

Your sites may have a wide variety of industrial applications and systems, and each application and system may have its own approved list of patches and upgrades. If your company is installing or evaluating NAC, your manufacturing IT organization should be prepared.

Two flavors of NACs

NACs come in two flavors, in-band and out-of-band. In-band systems are network appliances that are placed between access layer switches and distribution or core switches. They become a gate in the network: only systems that pass the admission tests can enter.

In-band systems can provide a fine level of control, granting access only to specific services or servers. However, in-band systems will require recabling in distribution switch cabinets. Out-of-band NAS systems attach to the network at a switch port and do not require recabeling. Out-of-band systems will be easier to install, especially on validated systems. But they do not provide the same level of granular control that in-band systems do, meaning they usually do not control port or server access.

The primary task for manufacturing IT in a NAC installation is the identification of the patch policies that should be enforced. This starts with an audit to identify all systems and software in use, and documentation of their application and O/S patch level. This information is then used to generate a security policy for each application.

There may be multiple security policies for each application, one for each patch level installed, because most sites will not be able to upgrade all copies of an application at the same time. Finally, when installing an O/S or application patch, you may have to change the application’s security policy.

NACs provide a valuable level of protection to corporate networks, but the cost will be added work during manufacturing system upgrades and patches.

Author Information

Dennis Brandl is president of BR&L Consulting, Cary, NC, which is focused on manufacturing IT solutions ( .

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