route from Rt1 before the variance is configured. Serial 0/0 is the only route to 192.168.30.0. Figure shows the output from show ip route from Rt1 after the variance is configured. The preferred route is interface FastEthernet 0/0, but Serial 0/0 will also be used. To verify load balancing, ping 192.168.30.1. After the ping is executed the preferred route is using interface Serial 0/0. IGRP will use load balancing between the two links. Web Links Using the Extended ping and Extended traceroute Commands http://www.cisco.com/en/US/tech/ tk826/tk365/ technologies_ tech_ note09186a0080093f22.shtml
Content 9.2 Network Testing 9.2.1 Introduction to network testing Basic testing of a network should proceed in sequence from one OSI reference model layer to the next. It is best to begin with Layer 1 and work to Layer 7 if necessary. Beginning with Layer 1, look for simple problems such as power cords plugged in the wall. 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 section focuses on network operations at a specific layer of the OSI model. The commands telnet and ping are two important commands that are used for testing a network. Interactive Media Activity Point and Click: Network Testing After completing this activity, the student will be able to understand network testing. Web Links Tools, Maintenance, and Troubleshooting Tips for Cisco IOS Software http://www.cisco.com/en/US/products/ sw/iosswrel/ps1828/prod_ troubleshooting_ technique09186a008010929b.html
Content 9.2 Network Testing 9.2.2 Using a structured approach to troubleshooting Troubleshooting is a process that allows a user to find problems on a network. There should be an orderly process to troubleshooting based on the networking standards set in place by an administration. Documentation is a very important part of the troubleshooting process. The steps in this model are:
  1. Collect all available information and analyze the symptoms of failure
  2. Localize the problem to within a single network segment, to a single complete module or unit, or to a single user
  3. Isolate the trouble to specific hardware or software within the unit, module, or user’s network account.
  4. Locate and correct the specific problem.
  5. Verify that the problem has been solved.
Figure shows another approach to troubleshooting. Neither of these concepts are the only methods to troubleshooting. However, the orderly process is of the utmost importance in order to keep a network running smoothly and efficiently. Using a structured approach to troubleshooting, every member of a network support team can know what steps each member of the team has completed to solve a problem. If a variety of troubleshooting ideas are tried with no organization or documentation, problem solving is not efficient. Even if a problem is solved in the non-structured environment, it will probably be impossible to replicate the solution for similar problems in the future. Interactive Media Activity Drag and Drop: Troubleshooting After completing this activity, the student will be able to understand show interface command. Web Links Tools, Maintenance, and Troubleshooting Tips for Cisco IOS Software http://www.cisco.com/en/US/products/sw/ iosswrel/ps1828/ prod_troubleshooting_ technique09186a008010929b.html
Content 9.2 Network Testing 9.2.3 Testing by OSI layers Testing should begin with Layer 1 of the OSI model and work to Layer 7 if necessary.Layer 1 errors can include: Layer 2 errors can include: Layer 3 errors can include: If errors appear on the network, the process of testing through the OSI layers should begin. The ping command is used at Layer 3 to test connectivity. At Layer 7 the telnet command may be used to verify the application layer software between source and destination stations. Both of these commands will be discussed in detail in a later section. Interactive Media Activity Matching: Testing with the OSI layers After completing this activity, the student will be able to understand the OSI layers. Web Links General Troubleshooting Tools http://www.nwnetsmart.com/ns/books/ ciscopress/samples/ 1578700922.pdf
Content 9.2 Network Testing 9.2.4 Layer 1 troubleshooting using indicators Indicator lights are a useful tool for troubleshooting. Most interfaces or NICs will have indicator lights that show whether there is a valid connection. Often this light is called the link light. The interface may also have lights to indicate whether traffic is being transmitted (TX) or received (RX). If the interface has indicator lights that do not show a valid connection, power off the device and reseat the interface card. A faulty or incorrect cable could also cause a link light to indicate a bad connection or no link.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 all switch or hub ports are in the correct VLAN or collision domain, and have appropriate options set for spanning tree and other considerations. Verify that the proper cable is being 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 connected and is in good condition. If there is doubt that the connection is good, reseat the cable and ensure that the connection is secure. Try replacing the cable with a known working cable. If this cable connects to a wall jack, use a cable tester to ensure that the jack is properly wired. Also check any transceiver in use to ensure that it is the correct type, is properly connected, and is properly configured. If replacing the cable does not resolve the problem, try replacing the transceiver if one is being used. Always check to make sure that the device is powered on. Always check the basics before running diagnostics or attempting complex troubleshooting. Web Links Installing and Troubleshooting Cabling and Network Boards http://home.att.net/~s.k.vincent/ 801_3.htm
Content 9.2 Network Testing 9.2.5 Layer 3 troubleshooting using ping The ping utility is used to test network connectivity. As an aid to diagnosing basic network connectivity, many network protocols support an echo protocol. Echo protocols are used to test whether protocol packets are being routed. The ping command sends a packet to the destination host and then waits for a reply packet from that host. Results from this echo protocol can help evaluate the path-to-host reliability, delays over the path, and whether the host can be reached or is functioning. The ping output displays the minimum, average, and maximum times it takes for a ping packet to find a specified system and return. The ping command uses