CCNA Study Notes - Using a Bridge and OSI Layers

There are a lot of software and hardware tools available for analyzing the performance of the net. Cisco IOS Commands Numerous features of the net operation and performance are visible with the "show" and "debug" commands. The "show" commands show the present state of interfaces, protocols, routing tables, CPU, memory and other hardware variables. The debug commands allow the network architect to observe the processing of info in real time. Software logging procedures save automatically important data for later analysis. IP Utilities and Tools The most useful net connectivity and reachability testing commands are ping and traceroute. Several other utilities and tools can help in understanding the functionality of a net. For instance, on a Microsoft Windows computer, netstat, nslookup, arp, and telnet can also test connectivity and reachability. Protocol Analyzers Protocol analyzers confirm that TCP/IP packets contain the right info. Protocol analyzers are able to detect particular TCP/IP traffic, such as broadcast and ARP, which is difficult to classify without examining data at the packet or frame level. Occasionally it is required to check network functionality in an environment that cannot be replicated by a model net. In this situation, the network architect can use a net simulation device. Network Simulation Devices Software applications can check theoretical models in a simulated environment. We can create network topologies with specific configurations and modify them very quickly. Network Simulation Devices can test nets that are very large to build as prototypes. The network administrator must determine the right tools to use for each test to demonstrate the net functionality. For instance, traceroute is a very handy tool for displaying the route path that a TCP/IP packet takes inside a network. On the other hand, it is not a good option for validating the configuration for route summarization. Stopping Device and Link Failures When a company adds software that needs high availability, the network architect increases redundancy to the network. From time to time this redundancy is increased without thinking what happens in a real network failure. It is significant to check how redundant links work during a failure situation. Experiments should measure how much time a net needs to stabilize after the redundant link becomes active. Redundant Links Model designs use numerous kinds of redundant links to check network availability. Redundant links can be used for failover and occasionally, for load balancing. Load Balancing Not all kinds of redundant links are able to support load balancing. Simple redundant links between Layer 2 switches cannot be used for load balancing. Equal cost routed links, and Layer 2 and Layer 3 links configured as part of an EtherChannel, can be used to load balance traffic during normal operation. They can also forward traffic in the event of a link failure.

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