troubleshooting Question

Testing DHCP failover - clients unable to contact the 'standby' DHCP server

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meirionwyllt asked on
Windows OSDHCPWindows Server 2012Windows Server 2019
12 Comments2 Solutions89 ViewsLast Modified:
Our main DHCP server is on Windows Server 2012 R2. We have a failover partner on Windows Server 2019. We have set up DHCP failover, which appears to be set up OK, because all the scopes are fully in sync, as are the leases.

I tried to test the failover, so I shut down the Active server. The Standby server was report Connection Interrupted. At this point, one of the test clients, I did ipconfig /all to test whether the client was at least point towards the Standby server, which it was. Also the DHCP Server logs in Event Viewer had events saying that "This DHCP server ###### has transitioned to a PARTNER DOWN state for the failover relationship #### and the MCLT period of 3600 seconds has expired. The server has taken over the free IP address pool of the partner server ##### for all scopes which are part of the failover relationship. So, all good I thought.

I then did an ipconfig /renew on this, but I got...

An error occurred while renewing the interface Ethernet : unable to contact your DHCP server. Request timed out.

Thinking that it could potentially be a port problem, I then did a telnet to the standby server on various ports (67,68,69) which all failed to connect (should the DHCP have allowed this telnet request to connect??)

In case it would make any difference, I clicked the 'Partner down' button on the Standby server in the Failover settings. It didn't make a difference. In fact, it was a bit annoying that I did that because after the Active server came back up it was in 'Recover wait' mode until the Maximum Client Lead Time elapsed, so for that time I had no functioning DHCP server at all!! It's back to 'Normal' now so that's fine, and it's giving out leases.

Anyway, I'm not sure what to try next. I've powered the Active server back up for now, and I can test again at a later point.

Any ideas what might be wrong here? I'm not sure if the problem is due to the failover not working, or due to a general DHCP server problem with the Standby server. Are there any other tests I can run to find out, before actually trying the failover test again?

Thanks.
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