Covers wireless and serial backhaul operation, client access, radio selection, enabling serial backhaul in radio profiles, and verification for robust mesh connectivity options.

A mesh serial backhaul is a wireless mesh networking feature that

enables separate uplink and downlink channels on dedicated radios to improve backhaul bandwidth
allows inbound and outbound traffic to use exclusive communication paths for better performance (one radio is used as the uplink radio and a different one is used as the downlink radio), and
supports universal access by extending network reach and avoiding shared-channel interference.

The Mesh Serial Backhaul feature is supported in the controller from Cisco IOS XE Cupertino 17.7.1 onwards for Cisco Catalyst 9124AXE outdoor APs. To enable this feature, associate a radio profile with a radio frequency (RF) tag. When you enable this feature, all APs with the same mesh profile share the mesh configuration. All APs with the same radio profile share the radio configuration.

The 2.4-GHz and 5-GHz radios, which are not used in serial backhaul, provide basic client access functionality. The downlink radio provides universal access.

Note

Slot 1 and slot 0 are supported as mesh backhaul. Slot 2 is not supported as a mesh backhaul. You can utilize slot 2 for client serving or for serial backhaul downlink.

Channel assignment

For the Mesh Serial Backhaul feature, channels are assigned according to these rules:

Uplink and downlink channels are different.
All the 5-GHz radios maintain a frequency guard between their operating channels. For example, 100-MHz channel spacing between radios in Cisco Catalyst 9124AXE outdoor APs.
Dynamic Frequency Selection (DFS) channels are supported.

In a root access point, the controller assigns channels because the uplink is wired. A mesh access point uses the last channel configured by the controller for this radio or uses the default channel. If the channel used by the MAP is not compatible with the uplink, the MAP picks a valid random channel and notifies the controller. In another scenario, when the MAP receives a channel change alert on the uplink radio, it randomly picks a new downlink channel. The MAP checks the validity of the downlink radio. If the current channel is not compatible, the MAP picks a random channel.

Prerequisites for channel assignment

Ensure that these prerequisites are met before channel assignment:

Enable tri-radio globally by running the Device# ap tri-radio command.
Enable the dual radio on the APs by running the Device# ap name ap-name dot11 5ghz dual-radio mode enablecommand.

Use cases

These are some of the use cases for the Mesh Serial Backhaul feature:

Maximize throughput : Serial backhaul allows the 5-GHz backhaul to operate on different channels, thereby maximizing throughput over multiple mesh hops.
Network segregation: APs that have serial backhaul enabled, segregate backhaul channel on mesh topographies. This avoids localized link interferences.

Enable serial backhaul in radio profile (GUI)

Enable mesh backhaul features on a specific radio profile to support serial backhaul in mesh deployments.

Procedure

	1.	Choose Configuration > Tags & Profiles > RF/Radio > Radio.
	2.	Click Add to add a radio profile. The Add Radio Profile page is displayed.
	3.	In the Add Radio Profile page, enter the name, and description.
	4.	In the Mesh Backhaul field, choose the Enabled radio button to enable the feature.
	5.	In the Mesh Designated Downlink field, choose the Enabled radio button to enable the feature. Note Mesh Designated Downlink is supported only on slot number 2 of Mesh APs. Radio profiles must be matched carefully to RF tag slots.
	6.	Click Apply to Device.

The radio profile is updated, enabling serial backhaul for selected mesh APs.

Enable mesh configurations in radio profile (CLI)

Configure your Cisco wireless AP to enable mesh backhaul and designate downlink radio slots in a radio profile.

Procedure

	1.	Enter global configuration mode. Example: `Device# configure terminal`
	2.	Configure wireless radio profile and enter the radio-profile configuration mode. Example: `Device(config)# wireless profile radio radio-profile-name`
	3.	Enable mesh backhaul. Example: `Device(config-wireless-radio-profile)# mesh backhaul` By default, this command is enabled. Mesh backhaul can be disabled on a specific slot, to stop the specific slot from being the backhaul candidate.
	4.	Enable the radio slot as a designated downlink. Example: `Device(config-wireless-radio-profile)# mesh designated downlink` By default, this command is disabled. It is enabled only for slot 2 of mesh APs. If another slot is configured as the designated downlink, a warning message appears: `Designated downlink is supported only on slot 2 of mesh APs. Associate in the RF tag accordingly.` By default, all the radio slots are mesh-enabled and not designated as downlink.

The mesh backhaul and designated downlink configurations are now applied to your selected radio profile.

Enable serial backhaul (CLI)

Configure a wireless profile to designate a radio as a mesh downlink backhaul.

Procedure

	1.	Enter global configuration mode. Example: `Device# configure terminal`
	2.	Configure the wireless RF tag to enter wireless RF tag profile configuration mode. Example: `Device(config)# wireless profile radio radio-profile-name`
	3.	Enable the specified radio as a designated mesh downlink backhaul. Example: `Device(config-wireless-radio-profile)# mesh designated downlink` The designated downlink is enabled in the radio profile only for slot 2.
	4.	Exit the submode and return to global configuration mode. Example: `Device(config-wireless-radio-profile)# exit`
	5.	Configure the wireless RF tag to enter wireless RF tag profile configuration mode. Example: `Device(config)# wireless tag rf rf-profile-name` The designated downlink is enabled in the radio profile only for slot 2.
	6.	Configure the designated downlink radio for serial backhaul. Example: `Device(config-wireless-rf-tag)# dot11 5ghz {slot1 \| slot2} radio-profile radio-profile-name` Note In mesh APs, the uplink and downlink are in the same slot by default. When you configure a designated downlink, the mesh AP is forced to use a specific radio as downlink.

The specified radio is now configured as a designated mesh downlink, and the mesh AP is forced to use that radio for downlink backhaul.

Fallback Mode

Note
If you configure at least one radio as a designated downlink, that radio will not be available for uplink. To prevent a configuration mistake, such as configuring the uplink radio as the designated downlink, the mesh AP uses a fallback timer. If the mesh AP cannot join the controller within 10 minutes, the designated configurations are cleared, and all radios become uplink-capable.

Device# configure terminal
Device(config)# wireless profile radio radio-mesh-downlink
Device(config-wireless-radio-profile)# mesh designated downlink
Device(config-wireless-radio-profile)# exit
Device(config)# wireless tag rf radio profile rf-map-tag
Device(config-wireless-rf-tag)# dot11 5ghz slot2 radio-profile radio-mesh-downlink

Mesh serial backhaul - configuration example

This example explains how to configure mesh APs to allow only slot 0 and slot 1 for backhaul connectivity:

Device# configure terminal
Device(config)# wireless profile radio radio-mesh-downlink
Device(config-wireless-radio-profile)# no mesh backhaul
Device(config-wireless-radio-profile)# exit

Device(config)# wireless tag rf rf-map-tag 
Device(config-wireless-rf-tag)# dot11 5ghz slot2 radio-profile mesh-disabled

Verify mesh serial backhaul

This reference provides commands to verify mesh AP serial backhaul configuration and operational status on wireless devices.

To verify mesh AP serial backhaul, run this command:

Device# show ap name MAP-SB config slot 2 | inc Mesh
Mesh Radio Role : Downlink Access
Mesh Backhaul : Enabled
Mesh Designated Downlink : Enabled

To verify serial backhaul enabled on a specific AP, run this command:

Device# show ap name MAP-SB mesh backhaul
MAC Address : 4cxx.4dxx.f4xx
Current Backhaul Slot: 1
Radio Type: Main
Radio Subband: All
Mesh Radio Role: Uplink Access <<<<<<
Administrative State: Enabled
Operation State: Up
Current Tx Power Level: 6
Current Channel: (104) <<<<<<
Antenna Type:
Internal Antenna Gain (in .5 dBm units): 1
MAC Address : 4cxx.4dxx.f4xx
Current Backhaul Slot: 2
Radio Type: Slave
Radio Subband: All
Mesh Radio Role: Downlink Access <<<<<<
Administrative State: Enabled
Operation State: Up
Current Tx Power Level: 8
Current Channel: (149) <<<<<<
Antenna Type:
Internal Antenna Gain (in .5 dBm units): 1

To verify mesh serial backhaul, run this command:

Device# show wireless profile radio detailed radio-mesh-downlink
Radio Profile name                              : radio-mesh-downlink
Description                                     :
Beam-Selection                                  : Not configured
Number of antenna to be enabled                 : 0
Mesh Backhaul                                   : Enabled
Mesh Designated Downlink                        : Enabled

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Mesh serial backhaul

Channel assignment

Prerequisites for channel assignment

Use cases

Enable serial backhaul in radio profile (GUI)

Procedure

Enable mesh configurations in radio profile (CLI)

Procedure

Example:

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Example:

Enable serial backhaul (CLI)

Procedure

Example:

Example:

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Mesh serial backhaul - configuration example

Verify mesh serial backhaul