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Setting up DHCP and DNS failover on two domain controllers

I currently have a network with a primary and backup domain controller.  For some reason the BDC was made to be the DNS and DHCP server.  Both DHCP and DNS are installed on the PDC and DNS on the PDC has been configured.  What I would liek to do is make the PDC the primary DHCP server and have the BDC work as the DHCP failover in the event the PDC crashes.  Is this as simple as configuring the PDC DHCP with the same settings as the BDC DHCP?  Does Windows server somehow know which server to use for DHCP services?  Any suggestions are greatly appreciated.
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PCNNY
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PCNNY
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1 Solution
 
CrashDummy_MSCommented:
Don't give both server exactly the same DHCP settings. They should be almost the same, difference being the scopes. Like if the subnet is 10.1.1.1 - 10.1.1.254, put half the scope on one server and half the scope on the other.
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drpoppersCommented:
You can't have two dhcp servers with the same address pools, the recommended microsoft way from what I remember, is to have two servers both running dhcp but with different address pools.

i.e. server a gives out 192.168.0.1- 192.168.0.50 server b gives out 192.168.1.51-192.168.1.100

It doesn't matter which server a client gets its address of if the other settings such as dns servers etc are the same for both servers. For dns just make sure the dns service is installed on both servers and give both address out in the dhcp options box.

Also if this is server 2003 as I think, PDC and BDC don't exist in the same way as they used to with NT. There are a few bits that are unique, google FSMO and you'll find loads of stuff on it.
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PCNNYAuthor Commented:
How does the network determine which DHCP server will be the primary though?  If I have two servers running DHCP and both have seperate address pools, I only want the PDC to be the active DHCP server and then and only then in the event of PDC crash, I want BDC DHCP server to kick in.  
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drpoppersCommented:
The dhcp server that responds first wins basically. You can't make it pick I'm afraid, dhcp failover isn't something the MS dhcp servers can do., I've seen it done with linux boxes with heartbeat scripts but it's not ideal in an AD environment.

What's the reason for only wanting one DHCP server? It doesn't hurt, honest.
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PCNNYAuthor Commented:
My confusion lies here.  
If I have two DHCP servers with different address scopes setup, then it is possible that some client PCs will have 192,168.0.1 and others will have 192.168.1.1.  Our firewall router LAN lets say is set to 192.168.0.1.  Won"t this be an issue for all the client PCs that are getting the 192.168.1.1 - dont they all need to be on the same network lan scope to communicate properly.  If I have my servers which have static IPs on 192.168.0.1-.15 and my client PCs end up getting 192.168.1.1-254, how will they be able to access the servers being that they are on different address pools?
Hope this makes sense.  
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drpoppersCommented:
You're correct, but you can split the pool from 192.168.0.16-192.168.0.60 on one server and 61-254 on the other one. They don't have to be different subnets and shouldn't be really as it could cause the issue you picked up. You can put the same reservations on both dhcp servers for the servers if you use them so that should be an issue ,you can back the settings up and copy this across and restore. NB dhcp backups only work to a local drive, not a network one for some bizarre reason.
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PCNNYAuthor Commented:
This sounds like a good solution except for one major problem.  I have over 150 client PCs and not enough ip addresses if I split the scope in half.  I almost need to do it the way you suggested before with two address scopes, but I have no idea jhow to do it and still be able to have both address scopes able to access all the static ip servers.  
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drpoppersCommented:
It doesn't actually matter if a client contacts server A and it's got no addresses left it will decline the request, the client willl rebroadcast and server B will pick it up and give an address out.

If you add a new subnet, you'll need to add a router for them to talk properly or you'll need to look at changing the IP range to a 172.16.x.x or a 10.x.x.x
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