DHCP reliability

[pran]

I just inherited a fairly medium-sized network (>500 workstations) on one broadcast domain. I plan to split this up into smaller subnets for better control and performance. The Windows 2008 R2 AD with 2 domain controllers is the least of my problem but what is bothering me is the lack of redundancy for the DHCP service which is really a major component. Other than putting the DHCP service in a 2008 cluster, what other methods are available to create a reliable DHCP service for a routed network?

[ChrisH]

Create 2 dhcp servers with the same config and then exclude a portion on one server and exclude the oposite portion of IPs on the other server. That way you will have 2 servers at all times and if one goes completely you can just make the excluded range available.
Make sure you define both DHCP servers on your routers/L3 switch under ip helper or whatever setting it is.

[pran]

Thanks ChrisH. Microsoft recommends 80/20 for this type of setup where 80% is served by one DHCP and the rest (20%) served by the other server. That still has holes since either of the two can go down and still leave the rest without services. I plan to buy 2 servers for virtualization, run VMWare and create a Windows 2008 R2 cluster using 2 virtual servers and then serve DHCP using that. Is this possible?

[cpjitservices]

Also of course the other option would be to not worry about your servers and do your DHCP through a router - we use Cisco 2600's fr DHCP - it is a lot of over head on the router but we have several of them doing different things. I think sometimes it's a bit easier because if a DHCP Server goes down IE you have DHCP being doled out through a Win 2008 server if that server goes down you've lost network access and I reckon a Server 2008 server is more likely to go down than a router.

We did have servers running DHCP, and found that if we took a server out of the network for maintenance even though we had another server to take the role we had problems with connectivity to the network on workstations. The routers seemed to be easier to configure and less to go wrong - we bought our Cisco 2620XM's off of eBay dirt cheap and they work flawlessly. We can remove a server for maintenance / repairs and not have to worry about other nodes connecting to the network.

Thats my opinion hope it helps