What is a KMS? KMS activates the clients operating system on your network instead of each client connecting to Microsoft. Running this nslookup command frequently reveals _vlmcs SRV entries that are tied to unauthorized Windows or Office KMS hosts. We have since fixed this by changing them to KMS clients. KMS (Key Management Service) is one of the methods to activate Microsoft Windows and Microsoft Office. Hosts activated via a KMS have to report back to a software license server once every 180 days. Service: _vlmcs; Protocol: _tcp; Priority and Weight can be ignored if there will be only one KMS host server in the environment.