DHCP Superscopes

Windows 2000 DHCP also has the ability to create 2 other types of scopes, one of which you may be familiar with, the other which is probably new to you. Superscopes were first introduced in Windows NT 4 SP2. Essentially, a superscope is used in situations where we run out of IP addresses on a subnet. For example, a network might be subnetted to allow only 254 hosts per subnet, and may be nearing (or have already passed) that number. As such, additional IP addresses are required. One solution would be to reevaluate our addressing scheme and by changing our mask values, make the subnets larger. However, this is not only impractical on a large network, but also often nearly impossible based on the size of such an undertaking. For this purpose, we can take two (or more) scopes and combine them into a single logical Superscope. This allows IP addresses from both scopes to be handed out on a single subnet. Of course, this presents an issue with local connectivity, since the second scope has addresses not considered local on the first subnet. For that reason, you need to ensure that important systems on that subnet (like your gateways or servers for example) are provided additional IP addresses to facilitate the necessary communication. To create a Superscope, right-click the DHCP server and choose ‘New Superscope’. The wizard that starts allows you to combine any number of existing scopes into a Superscope easily.

The second new type of scope in Windows 2000 DHCP is what is referred to as a Multicast scope. A multicast scope hands out addresses to multicast-enabled applications on the network. For those who are unsure about multicasts, a multicast is a type of data transmission where data is sent out by a host once, but received by many systems listening in on a single special IP address. These special addresses fall into the Class D range, which means their first octet ranges from 224-239, a range not valid for regular host addresses. Multicasts are usually used in conjunction with ‘streaming’ type applications, such as sending video and audio over the network. The benefit of multicasting is that only a single stream gets sent, and multiple systems receive the information – a much more efficient use of bandwidth than sending multiple streams simultaneously. Multicast scopes are often referred to as MADCAP – Multicast Address Client Allocation Protocol scopes. Note that in order to be able to obtain addresses from a MADCAP scope, a client application (such as NetMeeting) must support the MADCAP API.

Author: Dan DiNicolo

Dan DiNicolo is a freelance author, consultant, trainer, and the managing editor of 2000Trainers.com. He is the author of the CCNA Study Guide found on this site, as well as many books including the PC Magazine titles Windows XP Security Solutions and Windows Vista Security Solutions. Click here to contact Dan.