A scope is simply a range of IP addresses that a Dynamic Host Configuration Protocol (DHCP) server is configured to distribute. In the simplest case, where a single DHCP server oversees IP configuration for an entire subnet, the scope corresponds to the subnet.
However, if you set up two DHCP servers for a subnet, you can configure each with a scope that allocates only one part of the complete subnet range. In addition, a single DHCP server can serve more than one scope.
You must create a scope before you can enable a DHCP server. When you create a scope, you can provide it with the following properties:
A scope name, which helps you to identify the scope and its purpose
A scope description, which lets you provide additional details about the scope and its purpose
A starting IP address for the scope
An ending IP address for the scope
A subnet mask for the scope
You can specify the subnet mask with dotted-decimal notation or with network prefix notation.
One or more ranges of excluded addresses
These addresses won’t be assigned to clients. For more information, see the section “Feeling excluded?” later in this chapter.
One or more reserved addresses
These are addresses that will always be assigned to particular host devices. For more information, see the section “Reservations suggested” later in this chapter.
The lease duration, which indicates how long the host will be allowed to use the IP address
The client will attempt to renew the lease when half of the lease duration has elapsed. For example, if you specify a lease duration of eight days, the client will attempt to renew the lease after four days pass. This allows the host plenty of time to renew the lease before the address is reassigned to some other host.
The router address for the subnet
This value is also known as the Default Gateway address.
The domain name and the IP address of the network’s DNS servers and WINS servers