A wireless intrusion detection system (WIDS) monitors wireless network traffic and analyzes its wireless networking protocols to identify suspicious activity. The typical components in a WIDS are the same as an NIDS: consoles,database servers (optional), management servers, and sensors. However, unlike an NIDS sensor, which can see all packets on the networks it monitors, a WIDS sensor works by sampling traffic because it can only monitor a single channel at a time. The longer a single channel is monitored, the more likely it is that the sensor will miss malicious activity occurring on other channels. To avoid this, sensors typically change channels frequently, so that they can monitor each channel a few times per second.

Wireless sensors are available in multiple forms. A dedicated sensor is a fixed or mobile device that performs WIDS functions but does not pass network traffic from source to destination. The other wireless sensor forms are bundled with access points (AP) or wireless switches. Because dedicated sensors can focus on detection and do not need to carry wireless traffic, they typically offer stronger detection capabilities than wireless sensors bundled with AP or wireless switches. However, dedicated sensors are often more expensive to acquire, install, and maintain than bundled sensors because bundled sensors can be installed on existing hardware, whereas dedicated sensors involve additional hardware and software. Organizations should consider both security and cost when selecting WIDS sensors.

WIDS components are typically connected to each other through a wired network. Because there should already be a strictly controlled separation between the wireless and wired networks, using either a management network or a standard network should be acceptable for WIDS components. Choosing sensor locations for a WIDS deployment is a fundamentally different problem than choosing locations for any other type of IDS sensor. If the organization uses termdefwireless local area networks (WLAN), wireless sensors should be deployed so that they monitor the range of the WLANs. Many organizations also want to deploy sensors to monitor parts of their facilities where there should be no WLAN activity, as well as channels and bands that the organization's WLANs should not use. Other considerations for selecting sensor locations include physical security, sensor range, wired network connection availability, cost, and AP and wireless switch locations.

WIDSs provide several types of security capabilities. Most can collect information on observed wireless devices and WLANs and perform extensive logging of event data. WIDSs can detect attacks, misconfigurations, and policy violations at the WLAN protocol level. Organizations should use WIDS products that use a combination of detection techniques to achieve broader and more accurate detection. Examples of events detected by WIDSs are unauthorized WLANs and WLAN devices, poorly secured WLAN devices, unusual usage patterns, the use of active wireless network scanners, denial of service attacks, and impersonation and man-in-the-middle attacks. Most WIDS sensors can also identify the physical location of a detected threat by using triangulation.

Compared to other forms of IDS, WIDS is generally more accurate; this is largely due to its limited scope (analyzing wireless networking protocols). WIDSs usually require some tuning and customization to improve their detectionaccuracy. The main effort is in specifying which WLANs, APs, and STAs are authorized and in entering the policy characteristics into the WIDS software. Besides reviewing tuning and customizations periodically to ensure that they are still accurate, administrators should also ensure that changes to building plans are incorporated occasionally. This is needed for accurate identification of the physical location of threats and accurate planning of sensor deployments.

Although WIDSs offer robust detection capabilities, they do have some significant limitations. WIDSs cannot detect certain types of attacks against wireless networks, such as attacks involving passive monitoring and off-line processing of wireless traffic. WIDSs are also susceptible to evasion techniques, especially those involving knowledge of a product's channel scanning scheme. Channel scanning can also impact network forensics because each sensor sees only a fraction of the activity on each channel. WIDS sensors are also susceptible to denial of service attacks and physical attacks.

WIDS sensors can offer intrusion prevention capabilities. Some sensors can instruct end points to terminate a session and prevent a new session from being established. Some sensors can instruct a switch on the wired network to block network activity for a particular wireless end point; however, this method can only block wired network communications and will not stop an end point from continuing to perform malicious actions through wireless protocols. Most IDS sensors allow administrators to specify the prevention capability configuration for each type of alert. Prevention actions can affect sensor monitoring; for example, if a sensor is transmitting signals to terminate connections, it may not be able to perform channel scanning to monitor other communications until it has completed the prevention action. To mitigate this, some sensors have two radios—one for monitoring and detection and the other for performing prevention actions. When selecting sensors, organizations should consider what prevention actions may need to be performed and how the sensor's detection capabilities could be affected by performing prevention actions.