How does KMS work?

Similar to ADBA, KMS also requires the installation of a KMS host key (see Figure 5.16) to enable KMS functionality. With a dynamic DNS enabled, the KMS activation server automatically creates a service record (SRV) in DNS. Then, KMS clients over the RPC 1688 TCP port use the resource records in DNS to locate the KMS host and request activation. As with ADBA, activation over KMS requires no action from users either. Unlike ADBA, where activation lasts 180 days and client computers are bound to being a member of the domain, in KMS, where activation also lasts for 180 days, the reactivation of client computers is effected via attempts to renew with the KMS host every seven days by default. Since there is no such thing with ADBA, in KMS, there is something called threshold, which represents the minimum activation requirements. The threshold applies to both physical and virtual client machines and servers:

Figure 5.16: Installing a KMS host key while configuring a KMS activation server
The KMS threshold is an essential requirement where more than 25 physical or virtual Windows client OSes, or five MS Office clients, or five Windows Server KMS licenses, need to be in an organization's networking environment before system administrators can begin activating any computer over KMS.
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