Conventional wisdom holds that network reliability is typically 3-9s (99.9%) on a LAN, and 2-9s (99%) on a WAN. The leading causes of network failure are a WAN link failure, administrator error, cable failure, issues that involve connecting new devices or services, and malicious activity, including DoS attacks, worms, and viruses. Somewhere lower down on the list are equipment failures. To achieve the highest levels of availability, it is important that a strong change control policy and network management strategy be implemented.

There are numerous techniques for improving the reliability of data networks, including spanning tree, self-healing routing protocols, network management, and change control.