Cisco Network Troubleshooting Guide
Not only has the dependency for network grown, but the industry also is moving toward increasingly complex environments, involving multiple media types, multiple protocols, and often interconnection to unknown networks. These unknown networks may be defined as a transit network belonging to a Internet service provider (ISP), or a telco that interconnects private networks. The convergence of voice and video into data networks has also added to the complexity and the importance of network reliability. More complex network environments mean that the potential for connectivity and performance problems in internetworks is high, and the source of problems is often elusive.