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DHCP in use and already have scope , reservations, and MAC filtering need to add redundancy

Hi, We already have DHCP installed and running on a Domain Controller , Windows Server 2008 Standard  SP1 64 bit O/S.  This server also has Active Directory and dns.  The DHCP scope is already defined and has several reservations. Also it is using MAC filtering.  There is a second Windows 2008 server as a Domain Controller , running dns and Active Directory. So we need to implement DHCP redundancy or cluster or a backup failover DHCP server. What is recommended and not sure adding to or splitting the DHCP scope would be an option as need to have reservations and MAC filtering.  An automated solution would be nice but is it possible to implement without changing the current working DHCP server ?
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norcalty
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Split scope probably the easiest to manage.

You create the same scope on both DHCP servers, then exclude the lower half on one, and the upper half of the IP range on the other.

You make the same reservations on both DHCP servers, so no matter which one they attach to the client will get the reservation.

We do this and it works very well.
I'd like to mention that in smaller environments typically you don't setup DHCP failover unless you have some outstanding circumstances like running a 24/7 shop.  Since you have only two servers mentioned I'm assuming your environment is smaller.

 It's so easy to setup DHCP quickly that I usually just install DHCP on another server and document the settings.  It's about 5 minutes to setup a new one and authorize it as a DHCP server.
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Thanks for the responses.  We do run 24/7 and DHCP shows 984 in use.  I mentioned the second Windows 2008 server only to reference that we can implement DHCP on that server but we are trying to determine how best to do that. As you all have mentioned and having read other articles there are different approaches. Given that we use some reservations and we have to add every MAC address in a file for MAC filtering and several staff members do this the dual entry probably would not be feasible. We are simply looking for a means to have fault tolerance on DHCP, it would be nice if there was an automated Primary Secondary. How can we easily get DHCP to run from another Server without making changes to the scope on the Primary in the event that the Primary is not available?
The only way to do that is clustering the two machines as in the first example.  You must have shared storage to do this which will create another single point of failure without a secondary.  You can do it this way, it's just less common, more complicated and difficult and more expensive.
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How many computers?

Split the Address Pool, not the scope.
Hi, regarding the nightly export , how would you suggest managing the reservation list and MAC list ? Thanks
Thanks for the feedback and suggestions.