DHCP failover configuration question

We have two sites connected by a 100mb MPLS.  Our current DHCP config is that we have a DHCP server in each site and the scopes are split.

I am moving DHCP to two 2012 servers and want to use HA DHCP.

My question is do I do load balancing or hot standby?

I'm leaning toward hot standby and let both sites pull from site 1 as primary and make site 2 my standby.  Of course that means all of the site 2 PCs will be pulling IPs across the LAN, but it's not like it's a lot of traffic.

Thoughts on best way to set up DHCP HA with two sites?


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Will SzymkowskiSenior Solution ArchitectCommented:
I never encourage a hot standby. This is because you have additional hardware that is just sitting there doing nothing. Why not leverage both servers? This also helps the load as well because both servers are processing leases. Another thing is what happens if you lose the MPLS users at your site will not get any new DHCP leases and when leases start to expire they will not be able to be renewed.


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Cliff GaliherCommented:
You usually don't want the same scopes in two different sites. So in this case I wouldn't even recommend looking at DHCP failover.
crp0499CEOAuthor Commented:
Cliff, I'm curious about your thinking here.  From what I have read, the HA for DHCP is something that multi-site admins have really been wanting to have.  It seems all the rage really for redundancy.  Having the HA means if I lose my DHCP server in one site, there is still a server that can serve both sites.  

Even now, we have DHCP servers in both sites and both servers have all scopes on them, but they are manually split so as to avoid duplicate IPs being issued.

Can you expand more on your thinking?
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crp0499CEOAuthor Commented:
Will, our DHCP is running on our DCs so the server in site 2 that is hosting DHCP failover is still the DC for that site and the DFS namespace holder as well.
Will SzymkowskiSenior Solution ArchitectCommented:
If you are in a hot standby and your MPLS connection goes down users at Site2 are going to get their IP lease how?

Cliff GaliherCommented:
If you've configured both scopes and have IP helpers, you can do this. But that wasn't really the topology you initially described. If you go that route, two failover relationships in hot standby (one per scope, one each direction) usually makes more sense for latency reasons.
crp0499CEOAuthor Commented:
WOW...I just figured out that the DHCP HA is per scope, not per server!

I was expecting to build one server, add all of my scopes to that and then "replicate it" to the other server, but that's not how it works at all.  I can configure each scope differently.  That gives me more control over what I need\want to do, and Will's comment is spot on...if I lose the MPLS, which happens, I'm toast in the hot standby.

That being said, I still don't want to configure separate and independent DHCP servers in each site like I'm all olde school and all so I think I'll go with load sharing and split my percentages based on the resources in each site.

Thanks guys.  Both of you helped me in my understanding a great deal.
Cliff GaliherCommented:
That's why I said you'd configure TWO failover relationships. Server 1 can be active for site 1 and a hot standby for site 2. Server 2 can be active for site 2 and a hot standby for site 1. If your link fails, each server is still active for its own site. The hot standby only kicks in if a server fails and the link is up. Then it can handle both sites. If a server *and* the link fails, you'll suffer an outage, but you would anyways with any configuration.
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