1. 1 © 2004, Cisco Systems, Inc. All rights reserved. CCNA 2 v3.1 Module 9 Basic Router Troubleshooting

2. 222 © 2004, Cisco Systems, Inc. All rights reserved. Objectives

3. 333 © 2004, Cisco Systems, Inc. All rights reserved. The show ip route Command The show ip route command displays the contents of the IP routing table.

4. 444 © 2004, Cisco Systems, Inc. All rights reserved. Static Routing

5. 555 © 2004, Cisco Systems, Inc. All rights reserved. Dynamic Routing

6. 666 © 2004, Cisco Systems, Inc. All rights reserved. Default Route

7. 777 © 2004, Cisco Systems, Inc. All rights reserved. Configuring a Default Route This command does not work with IGRP

8. 888 © 2004, Cisco Systems, Inc. All rights reserved. Determining Route Source and Destination The network layer provides best-effort, end-to-end, packet delivery across interconnected networks. The network layer uses the IP routing table to send packets from the source network to the destination network.

9. 999 © 2004, Cisco Systems, Inc. All rights reserved. Determining L2 and L3 Addresses

10. 10 © 2004, Cisco Systems, Inc. All rights reserved. Determining Administrative Distance

11. 11 © 2004, Cisco Systems, Inc. All rights reserved. Determining the Route Metric Routing protocols use metrics to determine the best route to a destination.

12. 12 © 2004, Cisco Systems, Inc. All rights reserved. IGRP Metric Metric=K1 *Bandwidth + (K2 * Bandwidth)/256-load) + K3 * Delay The default constant values are K1=K3=1 and K2=K4=K5=0 so: Metric=Bandwidth + Delay

13. 13 © 2004, Cisco Systems, Inc. All rights reserved. Determining the Route Next Hop 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.

14. 14 © 2004, Cisco Systems, Inc. All rights reserved. Determining the Last Routing Update Use the following commands to find the last routing update: show ip route show ip route network show ip protocols show ip rip database

15. 15 © 2004, Cisco Systems, Inc. All rights reserved. Observing Multiple Paths to a Destination Some routing protocols support multiple paths to the same destination. Unlike single path algorithms, these multi- path algorithms permit traffic over multiple lines, provide better throughput, and are more reliable.

16. 16 © 2004, Cisco Systems, Inc. All rights reserved. Introduction to Network Testing

17. 17 © 2004, Cisco Systems, Inc. All rights reserved. Structured Approach to Troubleshooting

18. 18 © 2004, Cisco Systems, Inc. All rights reserved. Broken cables Disconnected cables Cables connected to the wrong ports Intermittent cable connection Wrong cables used for the task at hand Transceiver problems DCE cable problems DTE cable problems Devices turned off Typical Layer 1 Errors

19. 19 © 2004, Cisco Systems, Inc. All rights reserved. Improperly configured serial interfaces Improperly configured Ethernet interfaces Improper encapsulation set Improper clock rate settings on serial interfaces Network interface card (NIC) problems Typical Layer 2 Errors

20. 20 © 2004, Cisco Systems, Inc. All rights reserved. Routing protocol not enabled Wrong routing protocol enabled Incorrect IP addresses Incorrect subnet masks Typical Layer 3 Errors

21. 21 © 2004, Cisco Systems, Inc. All rights reserved. Layer 1 Problems in a Network

22. 22 © 2004, Cisco Systems, Inc. All rights reserved. Layer 3 Troubleshooting Using Ping

23. 23 © 2004, Cisco Systems, Inc. All rights reserved. Layer 7 Troubleshooting Using Telnet

24. 24 © 2004, Cisco Systems, Inc. All rights reserved. Troubleshooting Layer 1 Using show interfaces Command The show interfaces serial command

25. 25 © 2004, Cisco Systems, Inc. All rights reserved. Troubleshooting Layer 2 Using show interfaces Command The show interfaces command is perhaps the single most important tool to discover Layer 1 and Layer 2 problems with the router. The first parameter (line) refers to the physical layer. The second parameter (protocol) indicates whether the IOS processes that control the line protocol consider the interface usable.

26. 26 © 2004, Cisco Systems, Inc. All rights reserved. Troubleshooting Using show cdp neighbors Command

27. 27 © 2004, Cisco Systems, Inc. All rights reserved. Troubleshooting Using show cdp neighbors detail Command

28. 28 © 2004, Cisco Systems, Inc. All rights reserved. Troubleshooting Using traceroute Command

29. 29 © 2004, Cisco Systems, Inc. All rights reserved. Troubleshooting Routing Issues The show ip route Command

30. 30 © 2004, Cisco Systems, Inc. All rights reserved. Troubleshooting Routing Issues The show ip protocols Command

31. 31 © 2004, Cisco Systems, Inc. All rights reserved. Troubleshooting Using show controllers serial Command The show controllers serial Command

32. 32 © 2004, Cisco Systems, Inc. All rights reserved. Introduction to debug Debug syntax Warning: The debug all command should be used sparingly as this can disrupt router operations.

33. 33 © 2004, Cisco Systems, Inc. All rights reserved. Summary