Networking / Beginners

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IP Address Range

When defining the IP address range of a scope, you should use the consecutive addresses that make up the subnet for which you are enabling the DHCP service. However, you should also be sure to exclude from this defined range any addresses of statically configured computers already existing on your network. To exclude predefined addresses, you can simply choose to limit the scope range so that it does not include any statically assigned addresses. Alternatively, you can configure a scope that makes up the entire subnet and then immediately define exclusion ranges (see the next section) for all of the subnet's statically addressed computers.

One common method for handling the need for both static and dynamically assigned addresses within an address range is to reserve the first 10 addresses within any subnet for statically addressed servers and to begin the DHCP scope with the eleventh address. For example, in the subnet 192.168.1.0, you can keep the addresses 192.168.1.1 through 192.168.1.10 for your statically addressed servers, such as your DHCP server, your DNS server, your WINS server, and other servers with addresses that should not change. You can then define the addresses 192.168.1.11 through 192.168.1.254 as the range for the subnet's DHCP scope. (In another common implementation, the first 20 addresses are reserved for statically addressed servers.)

If servers on your network have already been configured with static addresses in the middle of the subnet range, such as 192.168.1.110 and 192.168.1.46, you should use exclusion ranges to keep these addresses from being assigned to other computers. Otherwise, because each subnet can use only a single range of IP addresses for its scope, you need to severely restrict the number of addresses available for lease.