They act like traffic cops, redirecting IP packets in a way that best utilizes server processing cycles. Vendors are starting to deliver systems that offer more sophisticated routing so companies can allocate resources at the application level. The devices can also be used to increase uptime. Before load balancers, companies relied on hot-swappable machines, which often required 15 minutes to reroute traffic in the event of a failure. With the Web, that's not acceptable.
Load balancers support live failover, so data is instantly transferred from machine to machine.
But selecting a load balancer presents Web-site managers with a dilemma. Most of the vendors delivering these systems are small start-up suppliers. The safe choice for network managers is Cisco, which markets Local Director and Distributed Director. Cisco is a known quantity with an established sales channel and support network. But some customers say the load balancers from the start-ups have more advanced features than those from Cisco, including application level routing, content management and security.