Configuring N+1 Backup
Context
N+1 backup allows multiple ACs to share one standby AC, which reduces AC purchase costs. ACs of different models can work in N+1 backup mode as long as they are running the same software version.
Pre-configuration Tasks
Before configuring N+1 backup, configure basic WLAN services on the active and standby ACs (For details, see Basic WLAN Service Configuration). The WLAN service configuration of the active and standby ACs must be consistent on the two ACs.
Procedure
The following configuration tasks can be performed in any sequence. Enabling N+1 Backup is performed after all configuration tasks are complete.
Configuring Option 43 on the DHCP Server
Context
If an AP and the ACs are located in different network segments, the AP cannot discover the ACs through broadcast after it obtains an IP address from the DHCP server. To address this problem, configure Option 43 on the DHCP server to advertise AC IP addresses to the AP.
After Option 43 is configured, the AP unicasts Discovery Request packets to the IP addresses carried in Option 43. If the IP addresses specified by Option 43 do not respond, the AP broadcasts Discovery Request packets to request IP addresses of the ACs in the local network segment. Option 43 only needs to carry addresses of the active and standby ACs for the AP and does not carry irrelevant active ACs' IP addresses, otherwise, the AP may not connect to the correct AC.
Usually, an independent device is used as a DHCP server. Perform correct configurations on the selected DHCP server. The following example uses a Huawei router as a DHCP server.
Procedure
- Run system-view
The system view is displayed.
- Run dhcp enable
DHCP is enabled.
By default, DHCP is disabled.
- Run ip pool ip-pool-name
The global address pool view is displayed.
- Run option 43 sub-option 2 ip-address ip-address &<1-8>
The Option 43 field is set to the IP addresses of the active AC and standby AC.
Configuring AC Roles (ACs on Different Network Segments)
Context
N+1 backup uses one standby AC to back up multiple active ACs. An AP determines AC roles based on AC priorities. It selects the AC with a higher priority as the active AC and the AC with a lower priority as the standby AC. The AP sets up a connection with the AC of the specified IP address.
Since the AP and ACs are on different network segments, the AP can discover only the two ACs specified in the Option 43 field. You only need to configure a global priority for each AC, so that the AP can determine the active and standby ACs by comparing their global priorities.
Procedure
- Configure the active AC.
Perform the following configurations on the active AC:
- Run ac protect priority priority
The global priority of the active AC is configured in the WLAN view.
By default, the AC priority in the WLAN view is 0.
The global priority of the standby AC must be smaller than that of the active AC.
A smaller priority value indicates a higher priority.
- Run ac protect priority priority
- Configure the standby AC.
Perform the following configurations on the standby AC:
- Run ac protect priority priority
The global priority of the standby AC is configured.
By default, the AC priority in the WLAN view is 0.
The global priority of the standby AC must be smaller than that of the active AC.
A smaller priority value indicates a higher priority.
- Run ac protect priority priority
Configuring AC Roles (ACs on the Same Network Segment)
Context
N+1 backup uses one standby AC to back up multiple active ACs. An AP determines AC roles based on AC priorities. It selects the AC with a higher priority as the active AC and the AC with a lower priority as the standby AC. The AP sets up a connection with the AC of the specified IP address.
ACs are on the same network segment as the AP. Therefore, the AP can discover all ACs. The AP may discover more than two ACs. If you only configure a global priority for each AC, the AP selects the AC with the highest global priority as the active AC, and may select an incorrect active AC. To ensure that the AP connects to the predefined active AC or standby AC, configure both the global priority and individual priority on the active AC, and configure only the global priority on the standby AC. Ensure that the ACs' priorities meet the following requirements: active AC's individual priority > standby AC's global priority > active AC's global priority.
If a global priority and an individual priority are both configured for an AP on the AC, the AC preferentially delivers the individual priority to the AP.
Procedure
- Configure the active AC.
Perform the following configurations on the active AC:
- Run ac protect priority priority
The global priority of the active AC is configured in the WLAN view.
By default, the AC priority in the WLAN view is 0.
Ensure that the ACs' priorities meet the following requirements: active AC's individual priority > standby AC's global priority > active AC's global priority.
A smaller priority value indicates a higher priority.
- Run priority priority-level
The individual priority of the AC is configured in the AP system profile.
By default, no AC priority is configured in the AP system profile view.
Ensure that the ACs' priorities meet the following requirements: active AC's individual priority > standby AC's global priority > active AC's global priority.
After you configure the AC's individual priority in the AP system profile, bind the AP system profile to an AP group.
- Run ac protect priority priority
- Configure the standby AC.
Perform the following configurations on the standby AC:
- Run ac protect priority priority
The global priority of the standby AC is configured.
By default, the AC priority in the WLAN view is 0.
Ensure that the ACs' priorities meet the following requirements: active AC's individual priority > standby AC's global priority > active AC's global priority.
- Run ac protect priority priority
Configuring Revertive Switchover
Context
After an active/standby AC switchover, the standby AC replaces the active AC and sets up a CAPWAP link with the AP to provide services. The AP periodically sends Primary Discovery Request packets to detect active AC status. If revertive switchover is enabled on the standby AC, the AP triggers a revertive switchover when it detects that the active AC recovers. The AP disconnects from the current AC and sets up a new CAPWAP link with the active AC. Resources on the standby AC are released and the standby AC then continues to provide backup services.
Revertive switchover needs to be enabled only on the standby AC.
Procedure
- Run system-view
The system view is displayed.
- Run wlan ac
The WLAN view is displayed.
- Run undo ac protect restore disable
Revertive switchover is enabled.
By default, global revertive switching is enabled.
If revertive switchover is disabled on the standby AC, traffic of an AP cannot be switched back to the original active AC even when the link between the original active AC and the AP restores.
(Optional) Configuring CAPWAP Heartbeat Detection
Context
As defined by CAPWAP, an AP and AC periodically exchange packets to maintain connectivity of the data channel and management channel. If the AP or AC does not receive any response from each other after CAPWAP heartbeat packets are sent for the specified number of times, the AP and AC consider the link between them disconnected.
Perform the following configurations on the active and standby ACs:
Procedure
- Run system-view
The system view is displayed.
- Run capwap echo { interval interval-value | times times-value } *
The CAPWAP heartbeat detection interval and number of heartbeat packet transmissions are configured.
By default, the CAPWAP heartbeat detection interval is 25s and the number of CAPWAP heartbeat detections is 6.
By default, if dual-link backup is enabled, the CAPWAP heartbeat detection interval is 25s and the number of CAPWAP heartbeat detections is 3.
If you set the CAPWAP heartbeat detection interval and the number of CAPWAP heartbeat detections smaller than the default values, the CAPWAP link reliability is degraded. Exercise caution when you set the values. The default values are recommended. If an AP goes offline unexpectedly, you can set a larger CAPWAP heartbeat detection interval and a larger number of CAPWAP heartbeat detections.
Enabling N+1 Backup
Context
After all N+1 backup configurations are complete, enable N+1 backup and then restart all APs to make the function take effect.
N+1 backup needs to be enabled on all ACs.
Procedure
- Run system-view
The system view is displayed.
- Run wlan ac
The WLAN view is displayed.
- Run undo ac protect enable
N+1 backup is enabled.
By default, N+1 backup is enabled.
- (Optional) Run ap-reset { all | ap-name ap-name | ap-mac ap-mac | ap-id ap-id | ap-group ap-group | ap-type { type type-name | type-id type-id } }
All APs are restarted to make the N+1 backup function take effect.
If N+1 backup is enabled, running the undo ac protect enable command does not restart online APs. You need to run the ap-reset { all | ap-name ap-name | ap-mac ap-mac | ap-id ap-id | ap-group ap-group | ap-type { type type-name | type-id type-id } } command to restart the APs and make the N+1 backup function take effect. You can also manually restart the APs to make the N+1 backup function take effect.
If the N+1 backup function is disabled, running the undo ac protect enable command restarts online APs. After the APs are restarted, the N+1 backup function starts to take effect.
If an AP goes online after N+1 backup is enabled, you do not need to restart the AP.
Verifying the N+1 Backup Configuration
Procedure
- Run the display ac protect command to check the N+1 backup status, AC revertive switchover status, the AC's global priority, and the standby AC's IP address.
- Run the display ap-system-profile { all | name profile-name } command to check the AC's individual priority for a specific AP and the standby AC's IP address.
