DHCP simplifies the task of allocating IP addresses to clients on a network (and to servers by using DHCP reservations), but large organizations can have multiple DHCP servers with each server having dozens or more scopes and each scope having its own special set of options. Similarly, DNS simplifies management of fully-qualified domain names (FQDNs) for both servers and clients, but large organizations can have multiple DNS servers with each one authoritative over dozens of zones and each zone containing thousands of resource records. How does one manage all this? On the Windows Server platform, you can use the DHCP Server snap-in to manage all the DHCP servers in your organization, but the snap-in really isn’t efficient when it comes to managing large numbers of DHCP servers. Similarly, you can use the DNS Server snap-in to manage all your DNS servers, but again this snap-in isn’t efficient for managing large numbers of DNS servers. For example, on large networks neither the DHCP snap-in nor DNS snap-in are very useful for helping you get quick answers to any of the following questions: ■■ ■■
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Which DHCP servers in my organization manage which blocks of the IP address space? Which IP addresses are actually being used at each site where my company has a physical presence? Which IP addresses have been assigned to virtual network adapters of virtual machines running on Hyper-V hosts? How can I modify a particular scope option for a certain number of scopes residing on several different DHCP servers? How can I determine which subnets of an IP address range being managed by a certain DHCP server are not being used? How can I determine how many free IP addresses are available for leasing for certain scopes on certain DHCP servers? How can I find all scopes that have 95 percent or more of their address pool leased out to clients? How can I track all the IP addresses that have been assigned over the last 12 months to a certain server on my network? How can I find DNS servers that don’t have a certain server option configured?
Administrators of large enterprises often want answers like these—and want them quickly. However, it can be difficult for them to keep track of their IP addressing schemes, DHCP server configurations, and DNS server configurations. Cloud hosting providers can have even greater difficulties keeping track of such information because their environments include both physical and virtual networks, and because of the address space reuse that often happens in multitenant cloud environments. In the past, most large enterprises and hosters have relied on either spreadsheets, custom software developed in-house, or third-party commercial programs for keeping track of IP addressing schemes, DHCP server configurations, and DNS server configurations. Beginning with Windows Server 2012, however, Microsoft introduced an in-box solution for performing these kinds of tasks. That in-box solution is IPAM. 106 Chapter 5
Networking