Points to Remember

• A complex network consists of multiple networks, connected with each other, using different types of links and a multi-protocol environment.

• Because of their multi-protocol architecture, complex networks have more problems as compared to independent LANs and WANs.

• Most complex networks have problems pertaining to the backbone network, transmission media, multiple networks and protocols, servers, and internal and external security mechanisms.

• There are three troubleshooting methodologies: Cisco hierarchical approach, layered approach and the problem resolution approach.

• In the hierarchical approach, you divide the network into three layers —Core Distribution and Access. This makes it possible to troubleshoot problems on each layer, without disturbing the entire network.

• In the layered troubleshooting approach, you isolate and troubleshoot the problem pertaining to a specific layer

• The Data-link layer enables node-to-node delivery of data in a network by converting bit streams received from the Network layer into manageable units.

• Problems at the Data-link layer usually pertain to the data loss or corruption. To counter this problem, protocols such as Unrestricted Simplex Protocol, Simplex Stop-and-Wait Protocol, and Sliding Window Protocol are used.

• Problems at the Network layer usually pertain to overloading of a specific transmission route, inappropriate subnet topology, dependency of the Network layer on the subnet topology and its number, and network congestion.

• To counter problems at the Network layer, the subnet topology should be independent of the Network layer. Similarly, routing algorithms should be used to ensure proper routing of data packets from the source to the destination network.

• In the problem resolution approach, you divide the entire troubleshooting process into a set of seven well-defined tasks : problem definition, facts collection, consideration of possibilities, action plan, definition, action plan implementation, observe and review findings, review problem solving cycle, isolation of error, resolve the problem.