NLB for High Availability
Applies To: Windows Server 2003 with SP1
Q. How Does NLB Detect a Server Failure?
A. While servicing client requests, each NLB Cluster host emits heartbeats to the other hosts in the cluster. If a host fails and stops emitting heartbeats, then after a default time period of five seconds, the remaining hosts in the cluster undergo a process called convergence to remove the failed host from the cluster and have new client connection requests mapped to remaining hosts in the cluster. So, new connections made by the client get handled by one of the remaining hosts in the cluster.
Q. How Long Does it Take For a Failed Server to be Removed From the Cluster?
A. By default, five seconds are required to detect a failed host. Once a failure is detected, the convergence process takes an additional two and a half to three seconds to evict the failed host and redistribute its load to the surviving hosts.