Dynamic Frequency Selection

Dynamic frequency selection

Dynamic Frequency Selection (DFS) is a process that

  • detects radar signals on DFS-enabled 5.0-GHz (802.11a/h) radios

  • automatically sets the frequency to avoid interference with radar signals, and

  • ensures radios configured for use in a regulatory domain do not interfere with radar systems.

Flex DFS behavior

In normal DFS, when a radar signal is detected on any of the channels in the 40-MHz or 80-MHz bandwidth, the whole channel is blocked. With Flex DFS, if the radar signals are not detected on the secondary channel, the AP is moved to a secondary channel with a reduction in the bandwidth, usually, by half.

Configure dynamic frequency selection (GUI)

Before you begin

Follow these steps to configure Dynamic Frequency Selection using GUI:

Procedure

Step 1

Choose Configuration > Wireless > Mesh > Profiles

Step 2

Choose a profile.

Step 3

In General tab, check the Full sector DFS status check box.

Step 4

Click Update & Apply to Device.

Configure dynamic frequency selection

Configure DFS to enable automatic radar detection and channel switching on 5 GHz wireless networks to comply with regulatory requirements.
Dynamic Frequency Selection (DFS) is required for 5 GHz wireless operations to detect radar signals and automatically switch channels when interference is detected. This ensures compliance with regulatory standards while maintaining network connectivity.

Before you begin

  • The corresponding AP must be on one of the DFS channels.

  • Shut down the radio before applying the configuration changes.

Procedure

Step 1

Enter global configuration mode.

Example:

Device# configure terminal

Step 2

Disable the 802.11a Dynamic Transmit Power Control (DTPC) setting.

Example:

Device(config)# no ap dot11 5ghz dtpc

Step 3

Configure the 802.11h channel switch mode.

Example:

Device(config)# ap dot11 5ghz channelswitch mode mode-num

Example:

Device(config)# ap dot11 5ghz channelswitch mode 1

Step 4

Configure the 802.11h power-constraint value.

Example:

Device(config)# ap dot11 5ghz power-constraint value

Example:

Device(config)# ap dot11 5ghz power-constraint 12

Step 5

Configure nonoccupancy time for the radar interference channel.

Example:

Device(config)# ap dot11 5ghz smart-dfs
Dynamic Frequency Selection is now configured, enabling automatic radar detection and channel switching to maintain regulatory compliance on 5 GHz wireless networks.

DFS verification

Use the following commands to verify the DFS configuration:

To display the 802.11h configuration, use the following command:

Device# show wireless dot11h

To display the auto-rF information for 802.11h configuration, use the following command:

Device# show ap auto-rf dot11 5ghz

To display the auto-rF information for a Cisco AP, use the following command:

Device# show ap name ap1 auto-rf dot11 5gh