Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 83 is the Cisco approved textbook to use alongside version of the Cisco Networking Academy Program CCNA 1 and CCNA 2 web-based courses. The topics covered provide you with the necessary knowledge to begin your preparation for the CCNA certification exam (640-801, or 640-821 and 640-811) and to enter the field of network administration. | Page 789 Tuesday May 27 2003 2 19 PM Introduction to Network Testing 789 Figure 18-3 shows one approach to troubleshooting network problems. Figure 18-3 OSI Layer Troubleshooting With a structured approach members of the network know what each member has completed to solve a problem. If a variety of ideas are used without any organization the problem solving becomes chaotic. Without a structured approach very few problems are solved. Page 790 Tuesday May 27 2003 2 19 PM 790 Chapter 18 Basic Router Troubleshooting The flowcharts in Figure 18-2 and Figure 18-3 are not the only methods of troubleshooting however the orderly process is very important to ensure that a network runs smoothly and efficiently. Testing by OSI Layers Testing should begin with Layer 1 of the OSI model and work to Layer 7 if necessary. Layer 1 physical layer errors can include the following Broken cables Disconnected cables Cables connected to the wrong ports Intermittent cable connection Wrong cables used for the task at hand must use rollovers crossover cables and straight-through cables correctly Transceiver problems Data communications equipment DCE cable problems Data terminal equipment DTE cable problems Devices turned off After exhausting all Layer 1 problems as possibilities for a network problem the next step is to investigate Layer 2 problem possibilities. Layer 2 errors can include the following Improperly configured serial interfaces Improperly configured Ethernet interfaces Improper encapsulation set High-Level Data Link Control HDLC is default for serial interfaces Improper clock rate settings on serial interfaces Network interface card NIC problems After exhausting all Layer 2 problems as possibilities for a network problem the next step is to investigate Layer 3 problem possibilities. Layer 3 errors can include the following Routing protocol not enabled Wrong routing protocol enabled Routing protocol incorrectly configured Incorrect IP addresses
