Hi Experts! The customer was reported experiencing issue with DHCP failover relationships, which is the backup /secondary DHCP server was unable to perform and operate after the active server which is the primary encountered a failure and problem. During that time multiple users are reportedly confirmed disconnected with their computer desktops. Appreciate if you can give what causes of this issue and best recommendation . DHCP Server Failover relationship getting Error: The Primary DHCP server fails to switch to partner server for redundancy and found not available. Current Setup : • DHCP failover relationships is on Hot standby Mode • Maximum Client Lead Time is set to default 1 hour. • State Switchover interval is set to 2 minutes. ( By default, 60 minutes) • Addresses reserved for standby server set to 10% . ( By default, 5%) • Failover relationships is both configured on the DHCP server – DC1(Active)and DC2 (redundancy) • Partner /standby server set to DC2.group.com ( Redundancy ) Findings: • KB 2919355 has been installed. Based on Microsoft reference new release of Latest Roll up update for Windows 2012 R2 is![34853-20291.jpg][1]![34854-statistics.jpg][2] KB2955135 which is not installed. • Server1 and Serve2 do not have same Statistics. • The standby server did not take the ownership of the whole DHCP scope because they need to wait for 1 hour based on MCLT settings. However, DHCP still perform renew leases and lease IP address to client using its own percentage of the scope within this hour. [1]: /answers/storage/attachments/34853-20291.jpg [2]: /answers/storage/attachments/34854-statistics.jpg Checked the following: • Check the failover state in the scope properties. – Working • Verified DHCP failover Time Synchronization between 2 servers. • Run the command in Powershell > Systeminfo /fo csv | ConvertFrom-Csv | select OS*, System*,Hotfix* | Format-List • No other sign or indicator of misconfigure DHCP failover Relationship • No DHCP Scope Policies found error and missing. • Addresses Reserved for Standby Server is set to 10% , by default 5% according to Microsoft. https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-r2-and-2012/dn338976(v=ws.11) Thanks