H

heartbeat

A special type of network packet that is sent out to each server node participating in a cluster to determine the responsiveness of a node. Server nodes that do not respond to heartbeat packets for a configurable period of time are marked as inactive.

hierarchical namespace

A namespace, such as with Domain Name System (DNS), that can be partitioned out in the form of a tree. This allows great flexibility in using a domain name, since any number of subdomains can be created under a parent domain.

hop

Used to describe how many routers a packet must travel through in order to reach its destination. For example, a message that passes through four routers is said to have taken four hops.