You should install the CU one by one. All the servers in your environment must install the same CU update.
The order for update is as below:
- If you want to update the PRStandard FE firstly, perform failover on it by this link: https://video2.skills-academy.com/en-us/skypeforbusiness/manage/ha-dr-and-backup-service/failing-over-and-failing-back-a-pool#fail-over-a-front-end-pool.
- Download CU 11 HF1 on PRStandard FE and install it following the steps that are described in Updates for Skype for Business Server 2015 (KB3061064).
- Fail back the PRStandard FE as this link: https://video2.skills-academy.com/en-us/skypeforbusiness/manage/ha-dr-and-backup-service/failing-over-and-failing-back-a-pool#fail-back-a-pool.
- Download CU 11 HF1 on DRStandard FE and install it following the steps that are described in Updates for Skype for Business Server 2015 (KB3061064).
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