The load balancing service dynamically handles the list of machines behind a given DNS alias. It distributes workload evenly across those machines, in order to get optimal resource utilization, maximize throughput, minimize response time, provide a fail-over mechanism and avoid overload.
Please find the user documentation in http://configdocs.web.cern.ch/configdocs/dnslb/index.html
The load balancing server uses load metrics to chose the most suitable nodes from all the available ones for a given alias and interact with the DNS servers so that the IP addres displayed by the alias are updated accordingly.
The Domain Name System (DNS), the de facto standard for name resolution and esential for the network, is an open standard based protocol which allows the use of names instead of IP addresses on the network. Load balancing is an advanced function that is provided by DNS, to allow sharing requests across several machines running the same service by using the same DNS name.