Managing HP Serviceguard for Linux, Seventh Edition, July 2007

Understanding Serviceguard Software Components
Responses to Failures
Chapter 388
Network Communication Failure
An important element in the cluster is the health of the network itself.
As it continuously monitors the cluster, each node listens for heartbeat
messages from the other nodes confirming that all nodes are able to
communicate with each other. If a node does not hear these messages
within the configured amount of time, a node timeout occurs, resulting in
a cluster re-formation and later, if there are still no heartbeat messages
received, a reboot.