DHCP Clustering in Windows 2000

[Scarpozzi]

I just started this fun little project yesterday. I installed Win2k Advanced Server on 2 systems and installed load balancing and clustering services. Has anyone else ever done this before? I'm using 2 P4 1.3gig Servers to do this and I have a Poweredge 4300 as my domain controller (probably going to use it as my external disk for the dhcp tables as well). I just need to know if anyone knows of a resource other than Microsoft's website for any possible problems I might encounter in the next day or so in getting a good working DHCP cluster. Both DHCP servers have 2 NICs in them and will be going out to the same switch. Any suggestions or help is greatly appreciated...

 

[Saltin]

DHCP isnt one of the services I would normally cluster. On my network, there are two subnets, and the routers are bootp compliant. I setup two DHCP servers with scopes set at 80/20. Even if one goes down, the other can still serve.

Those boxes you have are also a lot of juice for DHCP. It generally requires very little hardware wise.

 

[Scarpozzi]

True....However, clustering will provide superior redundancy. The machines are overkill, but this is in my test bed. I'd actually put these on some 1Us I have on a rack eventually. We've had problems in the past using the primary/backup approach...so we switched to Registrar for our DHCP and ended up with an even worse situation. This is just to replace everything and be done with it....we've got over 4000 client computers that hit us every day so we want it to be as stable as possible....

 

[Garion]

I'd be VERY cautious using a primary/secondary DHCP server. If they both have the same scopes defined and DON'T share the same database, you could get some very bad things happening. Example:

Server 1 hands out 10.1.1.51 to a computer at 9:00 AM
Server 1 crashes at 9:15 AM and Server 2 takes over
Server 2 assigns 10.1.1.51 to Computer B at 9:30 AM

You'll immediately start having massive IP address conflicts and things will pretty much grind to a halt, especially if you have a long lease time, like the MS default of three days. The only saving grace could be that MS does a ping of an IP before it assigns an address then tombstones that one and you have to manually restore it to "active" (unless MS has fixed that in 2K). You won't get any conflicts, but you'll rapidly run out of IP's.

This is a similar scenario to a DHCP server migration - The only way to do that is to trim your lease down to an hour or so, wait until the night and switch out the DHCP services to a new box.

IMHO, if you can cluster them and share a database, you're OK, as it will keep track of what it has. Not 100% sure about that tho.

Best solution - Have two DHCP servers and enough room in your scope that they can each have a totally independant range (server 1 has from .10 - .110, server 2 has from .111 - .220 or something). Probably too optimistic, but it's certainly good networking!

- G

 

[Saltin]

<< I setup two DHCP servers with scopes set at 80/20. Even if one goes down, the other can still serve >>



Is that what you mean Gar? When I say 80/20 I mean the scopes are split. There is obviously no overlap between the two servers.

 

[Garion]

Ahh. OK, then that's fine. As long as both have enough IP's to service all the users, you're probably OK. In that scenario, I'd bump UP the lease time. That way, if server #2 doesn't have enough IP's for everyone, you'll have a day or two to rebuild it the primary.

- G

 

[PeeluckyDuckee]

for clustering service in Advance Server don't you need scsi hardware? I get prompted for it when I try the setup.

what's the benefit of clustering DHCP vs the classic 80/20 method?

 

[Woodchuck2000]

Clustering DHCP is far more hassle than its worth, unless you have a seriously restricted scope. I'd agree with Garion, in that if you have a slight problem with one of your servers or with the database, you're going to get IP confilicts and I'm betting that your clients aren't going be smart enough to release and renew the lease if that happens.
Go with two separate scopes, it'll save hassle in the long run...

 

[Santa]

Since DHCP services is based on broadcast it is not a service ideal for clustering. Clustered services should be one in which the server needs to be fixed and the only way the client gets to the service is knowing where it is based on IP.


DHCP service is offered via the broadcast so basically as Garion said its best to just have multiple servers with difference scopes.. This is both redundant and safe whereas Cluster is perhaps redundant but may not be safe.

If you want to learn clustering try it with file and print sharing. This will be a much better implementation of cluster service since the client needs to know exactly where the file and print servers are exactly not via broadcast.

 

[Saltin]

<< what's the benefit of clustering DHCP vs the classic 80/20 method? >>



There isnt one, except being able to say you did it, I suppose : )

80/20 redundancy is about as fault tolerant as you can get, IMO.

 

[Scarpozzi]

I've been out of the office all week so we're going to start up Monday and get the working model finished by Tuesday hopefully as long as our other projects don't get in the way. From what I've learned from you guys though...I don't know if we'll actually implement this model to our network. I think we'll continue to research it. I appreciate all your posts...especially you Garion. Thanks! I am thinking if I set up two scopes like you suggested, this may be the best way to go, but I'd have to get it approved by our router admin...

If anyone has setup a DHCP service in a medium/large scale network, any advice would be appreciated as I'm still researching many options. Thanks.