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To track the activation threshold, the KMS host keeps a record of the KMS clients that request activation . The KMS host gives each KMS client a client machine identification (CMID) designation, and the KMS host saves each CMID in a table . Each activation request remains in the table for 30 days . When a client renews its activation, the cached CMID is removed from the table, a new record is created, and the 30-day period begins again . If a KMS client does not

renew its activation within 30 days, the KMS host removes the corresponding CMID from the table and reduces the activation count by 1 . The KMS host caches twice the number of CMIDs that KMS clients require to help ensure that the CMID count does not drop below the activation threshold . For example, on a network with clients running Windows 7, the KMS activation threshold is 25 . The KMS host caches the CMIDs of the most recent 50 activations . The KMS activation threshold for Windows Server 2008 R2 is 5 . A KMS host that is contacted only by clients running Windows Server 2008 R2 KMS would cache the 10 most recent CMIDs . If a client running Windows 7 later contacts that KMS host, KMS increases the cache size to 50 to accommodate the higher threshold . KMS never reduces the cache size .

KMS activation requires Transmission Control Protocol/Internet Protocol (TCP/IP) connectivity . By default, KMS hosts and clients use DNS to publish and find the KMS . The default settings can be used, which require little to no administrative action, or KMS hosts and clients can be configured manually based on network configuration and security requirements .

KMS activations are valid for 180 days . This is called the activation validity interval. To remain activated, KMS clients must renew their activation by connecting to the KMS host at least once every 180 days . By default, KMS client computers attempt to renew their activation every seven days . If KMS activation fails, the client will reattempt every two hours . After a client s activation is renewed, the activation validity interval begins again .

The KMS uses service (SRV) resource records (RRs) in DNS to store and communicate the locations of KMS hosts . KMS hosts use Dynamic DNS (DDNS), if available, to publish the KMS SRV RRs . If DDNS is not available, or the KMS host does not have rights to publish the RRs, the DNS records must be published manually or IT professionals must configure client computers to connect to specific KMS hosts . The Volume Activation Deployment Guide at http://go.microsoft.com/fwlink/ LinkId=150083 describes the steps necessary to publish the KMS in DNS .

By default, KMS clients query DNS for KMS information . The first time a KMS client queries DNS for KMS information, it randomly chooses a KMS host from the list of SRV RRs that DNS returns . The address of a DNS server containing the SRV RRs can be listed as a suffixed entry on KMS clients, which allows advertisement of SRV RRs for KMS in one DNS server and allows KMS clients with other primary DNS servers to find KMS . Also, priority and weight parameters can be added to the DnsDomainPublishList registry value for KMS . Doing so allows IT professionals to establish KMS host priority groupings and weighting within each group, which specify the KMS host to try first, to balance traffic among multiple KMS hosts . Only Windows 7 and Windows Server 2008 R2 use the priority and weight parameters . If the KMS host that a client selects does not respond, the KMS client removes that KMS host from its list of SRV RRs and randomly selects another KMS host from the list . After a KMS host responds, the KMS client caches the name of the KMS host and uses it for subsequent activation and renewal attempts . If the cached KMS host does not respond on a subsequent renewal, the KMS client discovers a new KMS host by querying DNS for KMS SRV RRs . By default, client computers connect to the KMS host for activation by using anonymous RPCs through TCP port 1688 . (IT professionals can change the default port .) After establishing a TCP session with the KMS host, the client sends a single request packet . The KMS host responds with the activation count . If the count meets or exceeds the activation threshold for that operating system, the client is activated and the session is closed . The KMS client uses this same process for renewal requests . The communication each way is 250 bytes .