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Cisco 3900 Series, Cisco 2900 Series, and Cisco 1900 Series Integrated Services Routers Generation 2 Software Configuration Guide
Chapter Configuring Radio Settings
Configuring Radio Channel Settings
DETAILED STEPS
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 2, 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.
Command Purpose
Step 1
configure terminal Enters global configuration mode.
Step 2
interface dot11radio {0 | 1} Enters interface configuration mode for the radio interface. The
802.11g/n 2.4-GHz radio is radio 0.
The 802.11n 5-GHz radio is radio 1.
Step 3
channel
{frequency | least-congested |
width [20 | 40-above | 40-below]
| dfs}
Sets the default channel for the wireless device radio.To search for
the least-congested channel on startup, enter least-congested.
Use the width option to specify a bandwidth to use. This option is
available for the Cisco 800 series ISR wireless devices and consists
of three available settings: 20, 40-above, and 40-below:
• Choosing 20 sets the channel width to 20 MHz.
• Choosing 40-above sets the channel width to 40 MHz with the
extension channel above the control channel.
• Choosing 40-below sets the channel width to 40 MHz with the
extension channel below the control channel.
Note The channel command is disabled for 5-GHz radios that
comply with European Union regulations on dynamic
frequency selection (DFS). See the “Enabling and
Disabling World Mode” section on page 279 for more
information.
Step 4
end Returns to privileged EXEC mode.
Step 5
copy running-config
startup-config
(Optional) Saves your entries in the configuration file.
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