Local load balancing provides a combination of greater capacity and high availability. The load balancing system presents a single external ip address known as a virtual server address. Client requests are redirected internally to an available physical server for fulfillment.
The load balancing function may be implemented by software such as Network Load Balancing Service(NLBS) shipped with Microsoft Windows Enterprise Server, or as load balancing appliances running the required load balancing software.
The limitation of local load balancing is that the origin servers must all be located in the same physical location. This means that the data center itself remains a single point of failure. A failure in any essential data center service will result in the site being unavailable.
In addition, a single physical location means that some clients will be affected by network latency due to their distant location.
The solution to the limitations of local load balancing is global load balancing. The single point of failure and network latency problems are eliminated by using geographically distributed server locations.