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Cisco IOS Software Configuration Guide for Cisco Aironet Access Points
OL-29225-01
Chapter 6 Configuring Radio Settings
Configuring Radio Channel Settings
Dynamic Frequency Selection
Access points with 5-GHz radios configured at the factory for use in the United States, Europe,
Singapore, Korea, Japan, Israel, and Taiwan now comply with regulations that require radio devices to
use Dynamic Frequency Selection (DFS) to detect radar signals and avoid interfering with them. When
an access points detects a radar on a certain channel, it avoids using that channel for 30 minutes. Radios
configured for use in other regulatory domains do not use DFS.
When a DFS-enabled 5-GHz radio operates on one of the 15 channels listed in Table 6-4, the access point
automatically uses DFS to set the operating frequency. When DFS is enabled, the access point monitors
its operating frequency for radar signals. If it detects radar signals on the channel, the access point takes
these steps:
• Blocks new transmissions on the channel.
• Flushes the power-save client queues.
• Broadcasts an 802.11h channel-switch announcement.
• Disassociates remaining client devices.
• If participating in WDS, sends a DFS notification to the active WDS device that it is leaving the
frequency.
• Randomly selects a different 5-GHz channel.
• If the channel selected is one of the channels in Table 6-4, scans the new channel for radar signals
for 60 seconds.
• If there are no radar signals on the new channel, enables beacons and accepts client associations.
• If participating in WDS, sends a DFS notification of its new operating frequency to the active WDS
device.
Note You cannot manually select a channel for DFS-enabled 5-GHz radios in some regions, depending on the
regulatory requirements. The access points randomly selects a channel in that case.
The full list of channels that require DFS is shown in Table 6-4.
For autonomous operation, DFS requires random channel selection among the channels listed in
Table 6-4. The channels not listed in Table 6-4 do not require random selection and may be manually
configured.
Channels requiring Dynamic Frequency Selection (DFS) may be manually selected for the 1040, 1130,
1140, 1230, 1240, 1250, 1260 and 1520 using the the -E or -M regulatory domains, or 1430 using -A,
-E, or -M domains. The same GUI/CLI used to manually configure non-DFS channels can be used to
select DFS channels as well. The default channel selection is "DFS", which randomly selects a channel.
Ta b l e 6-4 D F S Channel List
Channel Frequency Channel Frequency Channel Frequency
52 5260 MHz 104 5500 MHz 124 5620 MHz
56 5280 MHz 108 5520 MHz 128 5640 MHz
60 5300 MHz 112 5560 MHz 132 5660 MHz
64 5320 MHz 116 5580 MHz 136 5680 MHz
100 5500 MHz 120 5600 MHz 140 5700 MHz