DHCP Failover Problems

Question

_{Monday, February 25, 2013 9:24 AM}

We recently upgraded our DHCP servers to Windows Server 2012 and are taking advantage of the built-in DHCP failover. We have 2 servers, configured in Load Balance mode, 50/50 percentage split.

We are seeing errors in the event logs that suggest one scope is out of addresses:

DHCP client request from B8AC6F9F5B68 was dropped since the applicable IP address ranges in scope/superscope Central are out of available IP addresses. This could be because of IP address ranges of a policy being out of available IP addresses.

Looking on the 2 servers, against the scope that is reporting it is out of addresses, this is what I see.

Server 1:

Total Addresses: 42
In Use: 37
Available: 5
Addresses Available (this Server's pool): 0
Addresses Available (Partner pool): 5
Addresses Granted (this Server's Pool): 35
Addresses Granted (Partner pool): 2

Server 2:

Total Addresses: 42
In Use: 37
Available: 5
Addresses Available (this Server's pool): 0
Addresses Available (Partner pool): 5
Addresses Granted (this Server's Pool): 7
Addresses Granted (Partner pool): 30

I don't understand why there are 5 addresses but yet we continue to see the error messages in the event logs saying the scope is out of addresses.  Also, why do the figures for address available not make sense, eg: server 1 says it has no addresses in it's pool, 5 addresses in the partner pool, server 2 says the same...

All replies (3)

_{Wednesday, February 27, 2013 10:22 AM ✅Answered}

Hi,

Based on the following information, they did assign all 42 addresses.

Server 1:

Addresses Granted (this Server's Pool): 35

Server 2:

Addresses Granted (this Server's Pool): 7

However, it seems that server 1 thinks server 2 has only assigned 2 address, and server 2 thinks server 1 has only assigned 30 addresses. Both have the gap 5.

Server 1:

Addresses Granted (Partner pool): 2

Server 2:

Addresses Granted (Partner pool): 30

It is the reason that they both think that there are 5 addresses remain in partner's pool. But actually, all addresses have been assigned. There are 0 address remained in both server's pool so that they refuses the new DHCP request.

Best Regards

Scott Xie

Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.

_{Wednesday, February 27, 2013 5:43 PM ✅Answered}

Thanks.  We also found that the scopes where not replicating between DHCP servers.  That was down to us creating the failover relationship before installing a cumulative update for WS2012 - details here: http://support.microsoft.com/kb/2751456

Re-creating the failover relationship fixed the problem.

_{Wednesday, February 27, 2013 1:35 AM}

Hi,

Thank you for your question.

I am trying to involve someone familiar with this topic to further look at this issue. There might be some time delay. Appreciate your patience.

Thank you for your understanding and support.

Best Regards,

Aiden

If you have any feedback on our support, please click here

Aiden Cao
TechNet Community Support