DFS Rescan Hours

This parameter sets the hours (0-24) at which the device deletes the DFS database and performs a DFS rescan. The cron command options can be used to define the hour: For example, 1,6,13 to force a DFS rescan at 01:00h, 06:00h or 13:00h, or 0-23/4 for a DFS scan between 0:00h and 23:00h every 4 hours.

During the DFS rescan, the AP scans for as long as it takes to find the configured minimum number of free channels. You define the minimum number of free channels via the parameter 2.23.20.8.27 DFS-Rescan-Num-Channels. The device does not perform a DFS rescan If there has not yet been a forced change of channel and if at least the minimum number of free channels were found during the last DFS scan.

In some countries, the use of the DFS method for automatic channel selection is a legal requirement. With the DFS method (Dynamic Frequency Selection) an AP automatically selects an unused frequency, for example, to avoid interference from radar systems or to distribute WLAN devices as evenly as possible over the entire frequency band. When booting, the device randomly selects a channel from those available (based on the regional settings, for example). The device then checks whether there is a radar signal or another WLAN already on this channel. This scan procedure is repeated until a sufficient number of channels has been found that are free of radar signals and with the lowest possible number of other networks. The device then selects one of the free channels and observes it for 60 seconds to be sure there are no radar signals. For this reason, data traffic may be interrupted for a period of 60 seconds while the frequencies are scanned for a free channel.

By specifying certain times for the DFS rescan you reduce the chance of the 60-second scan occurring at an inappropriate time.