Methods for determining and utilizing server performance metrics in a network are provided. For example, such methods can involve determining the service availability and metric measurements of types of services provided by a content delivery machine. User weightings can be used to indicate whether more traffic should be sent to one content server address compared to another. DNS servers use the test result updates and/or user weightings to determine the best server to return in response to a request to resolve a given DNS name. Computer systems and apparatus for carrying out such methods are also provided.