Rogue Detection and Countermeasures 541Nortel WLAN Security Switch 2300 Series Configuration GuideRF Detection ScansAll radios continually scan for other RF transmitters. Radios perform passive scans and active scans:• Passive scans—The radio listens for beacons and probe responses.• Active scans—The radio sends probe any requests (probe requests with a null SSID name) to solicitprobe responses from other access ports.Passive scans are always enabled and cannot be disabled. Active scans are enabled by default but can bedisabled on a radio-profile basis.Radios perform both types of scans on all channels allowed for the country of operation. (This is the regulatorydomain set by the set system countrycode command.) 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 document EN 301 893. Section 4.6 of that documentspecifies requirements for Dynamic Frequency Selection (DFS). These requirements apply to radios operatingin the 5 GHz band (802.11a radios).In countries where Dynamic Frequency Selection (DFS) is required, WSS Software performs the appropriatecheck for radar. If radar is detected on a channel, the AP radio stops performing active scans on that channel inaccordance with DFS. However, the radio continues to passively scan for beacons from rogue devices.When an AP radio detects radar on a channel, the radio switches to another channel and does not attempt touse the channel where the radar was detected for 30 minutes. WSS Software also generates a message.Note. The Auto-RF feature must be enabled. Otherwise WSS Software cannot changethe channel.
