Checking over our DHCP server we were seeing quite a few of these errors appearing in the ‘Microsoft-Windows-DHCP Server Events/Admin’ event log:
Log Name: DhcpAdminEvents
Date: 1/28/2019 10:23:49 PM
Event ID: 20292
Task Category: DHCP Failover
User: NETWORK SERVICE
A BINDING-ACK message with transaction id: 943568 was received for IP address: 10.253.166.162 with reject reason: (Reject Reason Unknown ) from partner server: dc1.mydomain.com for failover relationship: dc1.mydomain.com-dc2.mydomain.com.
Researching this error I came across this forum post: https://social.technet.microsoft.com/Forums/en-US/15d00412-3dfc-4520-a74e-1f32fe1329ef/windows-server-2012-dhcp-event-id-20291?forum=winserveripamdhcpdns
Which lead me to this KB article: https://support.microsoft.com/en-ca/help/2955135/event-id-20291-is-logged-in-the-system-log-when-a-client-computer-is-m
The hotfix that Microsoft mentions is from November 2014 and has been installed on our server for a very long time. We never noticed this error back in 2014 when the hotfix was installed so we were not able to “first remove the failover relationship, install the update to both DHCP nodes and restart them, and then reestablish the failover relationship” per Microsoft’s article.
The article leads me to believe you have to deconfigure failover on all subnets, destroy the failover relationship, re-create the failover relationship and then re-configure failover on each subnet.
Turns out you can just right click ‘Deconfigure failover’ and then right click ‘Configure failover’ on the specific subnets having the issue and re-use the existing failover relationship to resolve this issue assuming you’ve installed the November 2014 hotfix.