Ensuring High Availability of DHCP using Windows Server 2012 DHCP Failover

re: Ensuring High Availability of DHCP using Windows Server 2012 DHCP Failover

teamdhcp — Tue, 09 Apr 2013 09:53:18 GMT

Hi Dan, Thanks for sharing your feedback. We have shared a script which is integrated with Windows task scheduler and provides for automatic synchronization of scope configuration like options, reservations, range etc. You can download it from -

gallery.technet.microsoft.com/.../Auto-syncing-of-configurati-6eb54fb0

Please do let us know if this will help address the scenarios that you pointed out.

re: Ensuring High Availability of DHCP using Windows Server 2012 DHCP Failover

Dan — Mon, 08 Apr 2013 22:21:49 GMT

Are there any plans to improve scope replication? Currently only replicating lease info is limiting. If we decide to change scope level DHCP options like:DNS, gateway, reservations, scope range... those all need to be manually replicated after the change, or manually set on both servers. If a change gets made on the scope on serverA, and a different change gets made on serverB forcing a scope replication will cause the change on one side to be deleted. In an environment where we have several admins making changes, I can see this leading to problems is adminA adds a reservation and replicates it, but doesn't know adminB made a change on the partner server, thus deleting adminB's change. All this info is replicated at cluster creation, why not put in a mechanism to always replicate it? Seems like a huge oversight to me.

re: Ensuring High Availability of DHCP using Windows Server 2012 DHCP Failover

teamdhcp — Thu, 04 Apr 2013 18:00:25 GMT

Hi Jlinesmn,

Yes. You can have school server as standby and central server as active.

re: Ensuring High Availability of DHCP using Windows Server 2012 DHCP Failover

jlinesnm — Thu, 04 Apr 2013 17:50:25 GMT

Thanks for this. One other question, can the setup be reversed? You describe the scenario for the schools being active and the central server being passive. Can we reverse that and have the central server be the active server and the school sites be passive and only become active if communication to the central server goes down?

re: Ensuring High Availability of DHCP using Windows Server 2012 DHCP Failover

teamdhcp — Thu, 04 Apr 2013 04:42:42 GMT

Hi Jlinesnm,

Yes - you can use active-passive (hot standby) mode or active-active (load balance) mode on more than 2 servers. But this will have to be for a different set of scopes. Here is how I see it getting deployed in your scenario. Lets say each of the 12 schools have few scopes/subnets e.g. School1_scope1 and School1_scope2 for school1. You will deploy one DHCP server at each of the 12 schools. The DHCP server at each school will have scopes of that school configured e.g. School 1 DHCP server will have School1_scope1 and School1_scope2. Likewise for each of the 12 schools. You will then configure a failover relation in hot standby mode from each of the school DHCP servers to the central DHCP server e.g you will create a failover relation - School1-Central which has School1_scope1 and School1_scope2 as part of that failover relation. Likewise for each of the 12 schools. The central DHCP server now will have 12 failover relations each of which is with a different school DHCP server. The central DHCP server will be standby server for each of the failover relation. The DHCP server at each school will have a single failover relation for which it will be the active server.

With this deployment, the DHCP server local to the school will lease IP addresses to the computers/devices at that school. If the DHCP server local to the school goes down, the clients at that school will get DHCP service from the central DHCP server which would have now turned "active" but only for the scopes of that specific school.

This deployment topology is referred to as hub-and-spoke. You can read a blog about it here - blogs.technet.com/.../multi-site-deployment-topologies-for-dhcp-failover.aspx.

You will need to ensure that the DHCP relays at each school are configured to relay DHCP client messages to both the DHCP servers - central server and local server.

Let us know if this deployment topology would work for you.

re: Ensuring High Availability of DHCP using Windows Server 2012 DHCP Failover

jlinesnm — Wed, 03 Apr 2013 22:57:06 GMT

Hi,

I was wondering if the Active-Passive mode can be used on more than two servers. We currently have a centralized DHCP server. One of our schools had their fiber cut and could not log in to local resources. We would have 12 schools that fall in to this scenario. So, could we set up Active-Passive with that many servers? Thanks.

re: Ensuring High Availability of DHCP using Windows Server 2012 DHCP Failover

teamdhcp — Fri, 29 Mar 2013 11:19:05 GMT

Hi David,

The statistics are not updated to reflect the fact that second DHCP server has taken ownership of the entire address pool of a scope. So, you will not see address available on the second server go to 100% after MCLT expiry in PARTNER DOWN state.

re: Ensuring High Availability of DHCP using Windows Server 2012 DHCP Failover

David — Wed, 27 Mar 2013 13:30:29 GMT

Hi,

I'm currently testing this new feature and It's a great improvement from clustering DHCP with 2008r2.

One issue though - I've configured a hot standby failover setup for my DHCP servers. For testing purposes I've set state switchover interval to 10mins, and MCLT to 5 minutes.

I see from the event logs the relationship status changes from:

NORMAL to COMMUNICATION_INT

then 10mins after:

COMMUNICATION_INT to PARTNER_DOWN.

Which is expected. However, 5mins after that I should expect my second DHCP server to take ownership of the scopes I've specified. However, the DHCP MMC snap in tells me that I only have 5% of address available in the secondary DHCP server's pool for both scopes. Am I right in assuming this should go to 100% after the MCLT time has expired?

Thanks,

re: Ensuring High Availability of DHCP using Windows Server 2012 DHCP Failover

teamdhcp — Mon, 18 Feb 2013 00:23:01 GMT

Hi Ross, DHCP failover does not provide for replication of server level/wide configuration. Allow/Deny MAC filter is a server level/wide configuration. The reason this is not provided for is because a DHCP serve can participate in more than one failover relationships with different partner DHCP servers. In such scenarios, replicating server level configuration can lead to undesirable resultant server level/wide configuration. If your server has a single failover relationship or a allow/deny MAC address filter list that applies to all servers, you can setup a regular sync between the DHCP servers by writing a simple PowerShell script and integrating it with Windows Task Scheduler so that it runs on a periodic basis.

Let us know if you have further questions.

re: Ensuring High Availability of DHCP using Windows Server 2012 DHCP Failover

Ross Harvey — Sun, 17 Feb 2013 21:48:27 GMT

Erm, replication of allow\deny MAC filter? I'm surprised this feature was completely missed out, we rely upon this in our organisation to prevent anyone from just plugging a device in, it seems this is the only aspect the Server 2012 replication doesnt handle, am I mistaken?

Thanks,

Ross