Application Delivery Controller (ADC), Global Server Load Balancer (GSLB), and methods for their operation in data networks are disclosed. The methods for load balancing may include receiving a query concerning a host name from a client, determining that there are two or more host servers associated with the host name, measuring various metrics associated with each of the two or more host servers and a local Doman Name Server (DNS), and based at least in part on the measurement, selecting a host server among the two or more host servers. The load balancing may also be based on a measured round trip time.