Refer below for detailed steps. You have to swap images once pre-download and initiate the failover, in order to reduce downtime.
https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/7-5/High_Availability_DG.html#pgfId-43571
Upgrade Procedure in HA Setup
Complete these steps:
1.After the WLCs are configured in the HA setup, the Standby WLC cannot be upgraded directly from the TFTP/FTP server.
2.Initiate upgrade on the Active WLC in the HA setup via CLI/GUI, and wait for the upgrade to finish.
3.Once the Active WLC executes all the upgrade scripts, it will transfer the entire image to the Standby WLC via the Redundant Port.
4.When the Standby WLC receives the image from the Active WLC, it will start executing the upgrade scripts. The transfer of the image to standby and the execution of the upgrade scripts on the Standby WLC can be seen on the Active WLC Console/Telnet/SSH/Http connection.
5.After a successful message of Standby Upgrade is observed on the Active WLC, it is important to issue the show boot command on the Active WLC in order to make sure the new image is set as the primary image.
6.Once verified, initiate primary image pre-download on the Active WLC in order to transfer the new image to all the APs in the network.
7.After pre-image is completed on all the APs, issue the show AP image all command in order to verify that the primary image on the WLC is set as the backup image on APs.
8.Initiate swap option to interchange the backup image as primary on the APs. With this implementation, the WLC's and AP's primary image is set to the new image.
9.Issue the schedule-reset command as per planned outage with the no swap option in order to reset the APs and WLCs so that they can boot with the new image.
10.All the APs will reboot and join the new Active WLC.
11.Issue the show boot, show sysinfo, show ap image all, and show redundancy summary commands in order to verify that both the WLCs and APs have booted with the new image.
Important Guidelines before Initiating a WLC Upgrade in HA Setup
- Service Upgrade is not supported in this release, so network downtime should be planned before you upgrade the WLCs in the HA setup.
- The peer should be in the Hot Standby state before you start the upgrade in the HA setup.
- It is recommended to reboot both the WLCs almost together after upgrade so that there is no software version mismatch.
- Schedule Reset applies to both the WLCs in the HA setup.
- The Standby WLC can be rebooted from the Active WLC using the reset peer-system command if a scheduled reset is not planned.
- Debug transfer can be enabled on the Active WLC as well as the Standby WLC.
- If Active WLC unexpectedly reboot between software download and reboot both WLCs, you need to reboot both WLCs in order to complete software upgrade.
HTH
Rasika
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