Configuring Scopes

A DHCP scope is a pool of IP addresses within a logical subnet, such as 192.168.0.11 through 192.168.0.254, that the DHCP server can assign to clients. Scopes provide the essential means for the server to manage distribution and assignment of IP addresses and of any related configuration parameters to clients on the network.

Tip When a DHCP server uses a given scope to assign addresses to clients on the local network, the server itself needs to be assigned an address that is compatible with that scope. For example, if a scope distributes addresses within the 192.168.1.0/24 range to the local network segment, the DHCP server interface facing that segment must be assigned a static address within the same 192.168.1.0/24 range.

An IP address within a defined scope that is offered to a DHCP client is known as a lease. When a lease is made to a client, the lease is active. Each lease has a specified duration, and the client must periodically renew the lease if the client is going to continue to use the address. The default lease duration value is eight days.

Leases can be renewed for a variety a reasons. First, a client automatically attempts to renew its lease after 50 percent of the client lease time elapses. A client also attempts to renew a lease upon restarting. When a DHCP client shuts down and restarts, it typically obtains a fresh lease for the same IP address it had prior to the shutdown. Finally, leases are refreshed when you execute the Ipconfig /renew command from a DHCP client computer.

You create scopes in DHCP by using the New Scope Wizard, which you can launch by right-clicking the DHCP server node in the DHCP console and then selecting New Scope from the Action menu.

The pages of the New Scope Wizard listed next allow you to configure the corresponding scope features:

• Scope Name page This page allows you to assign a name for the scope.
• IP Address Range page This page allows you to specify the starting and ending IP addresses that define the range of the scope, along with the subnet mask you want to assign to the distributed addresses.
• Add Exclusions page This page allows you to specify the IP addresses within the defined range that you do not want to lease to DHCP clients.
• Lease Duration page This page allows you to define the lease duration values. These lease durations are then assigned to DHCP clients.
• Configure DHCP Options page This page allows you to determine whether to configure DHCP options for the scope through subsequent pages in the New Scope Wizard or later (after the wizard has completed) through the DHCP console.
  Important If you select the option to configure DHCP options later, the wizard does not give you an opportunity to activate the scope. You must activate the scope manually before it can begin leasing addresses.
• Router (Default Gateway) page (optional) This page allows you to specify which default gateway (and alternates) should be assigned to DHCP clients.
• Domain Name And DNS Servers page (optional) This page allows you to specify both the parent domain to be assigned to client computers and the addresses of DNS servers to be assigned to the client.
• WINS Servers page (optional) This page allows you to specify the addresses of WINS servers to be assigned to the client. Clients use WINS servers to convert NetBIOS names to IP addresses.
• Activate Scope page (optional) This page allows you to determine whether the scope should be activated after the wizard has completed.

You can modify these features later through the DHCP console.