Layer 1 troubleshooting using indicators 9.2.4 The page will explain how to troubleshoot Layer 1 issues with the help of indicator lights. Most interfaces or NICs have indicator lights that show if there is a valid connection. This light is often called the link light. The interface may also have lights to indicate when traffic is transmitted (TX) or received (RX). If the interface has indicator lights that do not show a valid connection, check for faulty or incorrect cabling. If cabling is correct, power off the device and reseat the interface card. Check to make sure that all cables are connected to the appropriate ports. Make sure that all cross-connects are properly patched to the correct location using the appropriate cable and method. Verify that the proper cable is used. A crossover cable may be required for direct connections between two switches or hubs, or between two hosts such as PCs or routers. Verify that the cable from the source interface is properly con...
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Testing by OSI layers 9.2.3 This page will describe the types of errors that occur at the first three layers of the OSI model. Layer 1 errors can include the following: Broken cables Disconnected cables Cables connected to the wrong ports Intermittent cable connection Rollover, crossover, or straight-through cables used incorrectly Transceiver problems DCE cable problems DTE cable problems Devices turned off Layer 2 errors can include the following: Improperly configured serial interfaces Improperly configured Ethernet interfaces Improper encapsulation set Improper clockrate settings on serial interfaces Network interface card (NIC) problems Layer 3 errors can include the following: Routing protocol not enabled Wrong routing protocol enabled Incorrect IP addresses Incorrect subnet masks If errors appear on the network, the process of testing through the OSI layers should begin. The...
Using a structured approach to troubleshooting 9.2.2 Troubleshooting is a process that allows a user to find problems on a network. This page explains why an orderly process should be used to troubleshoot a network. This process should be based on the networking standards set in place by a network administrator. Documentation is a very important part of the troubleshooting process. The steps in this model are as follows: Step 1 Collect all available information and analyze the symptoms of the failure. Step 2 Localize the problem to a particular network segment, module, unit, or user. Step 3 Isolate the trouble to specific hardware or software within the unit, module, or user network account. Step 4 Locate and correct the problem. Step 5 Verify that the problem has been solved. Step 6 Document the problem and the solution. Another approach to troubleshooting. These are not the only ways to troubleshoot a network. However, an orderly process is important t...
Network Testing >Introduction to network testing 9.2.1 This page will give students an overview of how to test a network. Basic testing of a network should proceed in sequence from one OSI reference model layer to the next. Begin with Layer 1 and work up to Layer 7, if necessary. At Layer 1, look for simple problems such as power cords plugged in the wall and other physical connections. The most common problems that occur on IP networks result from errors in the addressing scheme. It is important to test the address configuration before continuing with further configuration steps. Each test presented in this lesson focuses on network operations at a specific layer of the OSI model. At Layer 3, the commands telnet and ping are used to test the network. The next page will discuss the troubleshooting process.
Observing multiple paths to destination 9.1.9 Multi-path algorithms permit traffic over multiple lines, provide better throughput, and are more reliable than single path algorithms. IGRP supports unequal cost path load balancing, which is known as variance. The variance command instructs the router to include routes with a metric less than n times the minimum metric route for that destination, where n is the number specified by the variance command. The variable n can take a value between 1 and 128, with the default being 1, which means equal cost load balancing. rt1 has two routes to network 192.168.30.0. The variance command will be set on rt1 to ensure that both paths to network 192.168.30.0 are utilized. Figure shows the output from show ip route from rt1 before the variance is configured. FastEthernet 0/0 is the only route to 192.168.30.0. This route has an Administrative Distance of 100 and a metric of 8986. Figure shows the output from show ip route from rt1 ...
Determining the route next hop 9.1.7 Routing algorithms fill routing tables with a variety of information. Destination next hop associations determine the best path and which router to forward the packet to next. This router represents the next hop on the way to the final destination. When a router receives an incoming packet, it checks the destination address and attempts to associate this address with a next hop. Determining the last routing update 9.1.8 show ip route show ip route address show ip protocols show ip rip database
Determining the route metric 9.1.6 Routing protocols use metrics to determine the best route to a destination. The metric is a value that measures the desirability of a route. Some routing protocols use only one factor to calculate a metric. For example, RIP v1 uses hop count as the only factor to determine the metric of a route. Other protocols base their metric on hop count, bandwidth, delay, load, reliability, and cost. Each routing algorithm interprets what is best in its own way. The algorithm generates a number, called the metric value, for each path through the network. A lower metric number generally indicates a better path. Factors such as bandwidth and delay are static because they remain the same for each interface until the router is reconfigured or the network is redesigned. Factors such as load and reliability are dynamic because they are calculated for each interface in real-time by the router. The more factors that make up a metric, the great...