In the previous installments to this article, I outlined how to install and authorize a DHCP server under Windows Server 2003. The work does not yet stop here because a DHCP server requires a scope or range of IP addresses to lease to DHCP clients. This article will outline some of the important information you need to remember about DHCP scopes.

As already mentioned, a DHCP server must be configured with at least one active scope before it can lease IP addresses to DHCP clients. A scope is a range, or pool, of IP addresses that can be leased to DHCP clients on a given subnet. If there are multiple subnets, a DHCP server must be configured with multiple scopes.

Scopes do not only contain IP addresses for DHCP clients. A scope can also include optional parameters such as the IP address of DNS servers, WINS servers, and routers. The optional parameters can then be given to DHCP clients when they lease an IP address.

Before you jump into the process of creating scopes (and tackle the exam), you should keep a few important points in mind:

• All DHCP servers on the network require at least one active scope.

• Any static IP addresses need to be excluded from the scope. This eliminates the possibility of one IP address being assigned to two computers.
• If necessary, a single DHCP server can have multiple scopes.
• Scope information is not shared between DHCP servers. IP addresses between scopes must not overlap

The 80/20 rule is a very popular exam topic. It is a method of providing redundancy on the network. With this configuration, 80% of the IP addresses for the local subnet are added to a scope on the local DHCP server, and the remaining 20% of the IP addresses are added to a scope for the same subnet on another DHCP server. In other words, 80% of the IP addresses are from the local subnet and 20% from a remote subnet. Because both servers have IP addresses available for the same subnet, clients can always obtain an IP address if one of the servers becomes unavailable (until the scope runs out of available addresses). Be familiar with this concept because you will likely run into a question dealing with redundancy between DHCP servers.