Microsoft: Setup DHCP Servers with Split Scope - 80/20 Rule

<< 80/20 Rule >>
You will probably install more than one DHCP server so that the failure of any individual server will not prevent DHCP clients from starting. However, DHCP does not provide a way for DHCP servers to cooperate in ensuring that assigned addresses are unique. Therefore, you must carefully divide the available address pool among the DHCP servers to prevent duplicate address assignment.

For balancing DHCP server usage, use the 80/20 rule to divide scope addresses between DHCP servers.


<< 80/20 Rule Model >>
DHCP Server 2 is configured to lease most (about 80 percent) of the available addresses. DHCP Server 1 is configured to lease the remaining addresses (about 20 percent).

This scenario allows the local DHCP server (DHCP Server 2) to respond to requests from local DHCP clients most of the time. The remote or backup DHCP server (DHCP Server 1) assigns addresses to clients on the other subnet only when the local server is not available or is out of addresses. This same rule can be used in a multiple-subnet scenario to ensure the availability of a DHCP server when a client requests a lease.

But how to install this DHCP server. In Windows 2003 it was a lot of work but now with Windows 2008 R2 is is much better,install one serve and get one for free, ok almost. Let me show you how to do this.

First you need two servers in the same domain with the DHCP role on it. Sure You can cluster the DHCP and the management is done on one console and if one DHCP server fails the fail-over will take place and the scopes are running on the second node.

Now two single servers with any scope rule you want.

After the add role the wizard popsup and want to configure the DHCP server , the listener address:

If you don’t want to configure the scope right now, do not add scope. Fill in the domain and use IPv6 or WINS if you want it:

Now that the DHCP server is running we do a Split Scope.

Right click on the scope and do a split-scope again the wizard pops-up

Fill in the second DHCP server with or without scopes and select your scope range I choose for the common 80/20 or better 73 /27 scope bet you are all using this.

In the delay time you can make sure that one server is a faster listener than the other.

As you can see there is no scope on the secondary node , now that the wizard is finished the scope is auto configured on the other node.

If you do this, make sure all the settings and reservations are set on the first node because there is no wizard that syncs the servers.