470 CHAPTER 11: DETECTING AND COMBATTING ROGUE DEVICESto a wireless laptop. Users can configure a wireless network interface card(NIC) in “ad hoc” mode and easily set up a simple peer-to-peer network.Although this WLAN might be isolated from the corporate WLAN, theusers are stealing the air from legitimate WLAN users. The private WLANcan also cause RF interference with an authorized WLAN in other parts ofthe company.RF Detection Scans All radios continually scan for other RF transmitters. Radios performpassive scans and active scans:■ Passive scans — The radio listens for beacons and probe responses.■ Active scans — The radio sends probe any requests (probe requestswith a null SSID name) to solicit probe responses from other accesspoints.Radios perform both types of scans on all channels allowed for thecountry of operation (set by the country code when you created thenetwork plan). 802.11b/g radios scan in the 2.4 GHz to 2.4835 GHzspectrum. 802.11a radios scan in the 5.15 GHz to 5.85 GHz spectrum.Both enabled radios and disabled radios perform these scans.Dynamic Frequency Selection (DFS)Some regulatory domains require conformance to ETSI documentEN 301 893. Section 4.6 of that document specifies requirements forDynamic Frequency Selection (DFS). These requirements apply to radiosoperating in the 5 GHz band (802.11a radios).In countries where Dynamic Frequency Selection (DFS) is required, MSSperforms the appropriate check for radar. If radar is detected on achannel, the MAP radio stops performing active scans on that channel inaccordance with DFS. However, the radio continues to passively scan forbeacons from rogue devices.Countermeasures You can enable MSS to use countermeasures against rogues.Countermeasures consist of packets that interfere with a client’s ability touse the rogue.Countermeasures are disabled by default. When you enable them, alldevices of interest that are not in the known devices list become viabletargets for countermeasures. The Mobility Domain’s seed WX switch
