How KMS Works
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 Activation Renewal
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 .
Publication of the KMS
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
NOTE DNS changes may take time to propagate to all DNS hosts, depending on the complexity and topology of the network.
Client Discovery of the KMS
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 .
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