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CCNA 2 v3.1 Module 9 Basic Router Troubleshooting

CCNA 2 v3.1 Module 9 Basic Router Troubleshooting. Objectives. One of the primary functions of a router is to determine the best path to a given destination. A router learns paths, also called routes, from an administrator's configuration or from other routers by way of routing protocols

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CCNA 2 v3.1 Module 9 Basic Router Troubleshooting

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  1. CCNA 2 v3.1 Module 9 Basic Router Troubleshooting

  2. Objectives • One of the primary functions of a router is to determine the best path to a given destination. • A router learns paths, also called routes, from an administrator's configuration or from other routers by way of routing protocols • This module will describe methods for examining and interpreting the contents of the routing table • Network testing and troubleshooting are perhaps the most time consuming components of every network administrator’s job. • Efficient testing and troubleshooting must be done in a logical, orderly, and well-documented fashion • This module will introduce several of the most important of these tools and provide practice in their use.

  3. The show ip route Command The show ip route command displays the contents of the IP routing table.

  4. Dublin# show ip route Networks being advertised Out interface Codes, how the routes were learnt Administrative Distance Metric Next Hop Time since last update Examining the Routing Table • A routing table contains a list of the best available routes. • Routers use routing tables to make packet forwarding decisions.

  5. Static Routing

  6. Dynamic Routing

  7. Default Route • Default routes are used when there isn’t a more specific entry in routing table. • The router uses the default route to reach the gateway of last resort.

  8. Configuring a Default Route • Alternatively use the default network command • Router(config)# ip default-network 172.16.1.2

  9. Determining Route Source and Destination

  10. Routing – Role of Layer 2 and Layer 3 Addressing 00:ac:2d:34:56:11 00:01:46:26:23:a4 192.168.1.5 192.168.3.10 00:01:46:26:23:a4 00:04:24:98:55:44 00:04:24:98:55:44 00:2a:3b:3c:a4:33

  11. Role of Packets and Frames in Path Traversal

  12. Determining L2 and L3 Addresses

  13. Determining Administrative Distance • AD measures the trustworthiness of the source of the route information. • The lower the AD, the more trustworthy the source. • Different routing protocols have different default ADs. • When there are two paths available to a destination the path with the lowest AD is used in the routing table.

  14. Determining the Route Metric • Routing algorithms generate a number, called the metric value, for each path through the network . • The metric value is used to determine the best route to a destination. • The various protocols base their metrics on different factors: 

  15. Routing Metrics • Hop Count • number of hops • Bandwidth • speed of the link • Delay • the time taken to traverse the path • Reliability • the error rate on a link, from 1(bad) to 255 (good). • Load • the amount of traffic on the link from 1(good) to 255(bad) • MTU • Largest packet allowed on link • Cost • Arbitrary meaning – assigned by administrator – lower is better

  16. RIP Hop Count IGRP Metric = [K1 * Bandwidth + (K2 * Bandwidth)/(256-load) + K3*Delay] * [K5/(reliability + K4)] Defaults: K1 = K3 = 1 and K2 = K4 = K5 = 0. If K5 = 0, then [K5/(reliability + K4)] =0. Metric = Bandwidth + Delay. Routing Metric Calculations

  17. Viewing the Routing Table • Use the following commands to find the last routing update: • show ip route • show ip route network • show ip route connected • show ip route static • show ip protocols • show ip rip database

  18. Show ip route Command

  19. 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.

  20. Introduction to Network Testing

  21. Structured Approach to Troubleshooting

  22. Typical Layer 1 Errors • 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

  23. Troubleshooting Usingshow interfaces • Useful for troubleshooting Layer1, Layer 2 in addition to Layer 3 addressing

  24. Physical layer (line status) Up: has Layer 1 connectivity Down: L1 problem Administratively down: disabled BHM# show interface s0 Serial0 is up, line protocol is up < output omitted > Last clearing of "show interface" counters never < output omitted > Received 73 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 135 packets output, 7361 bytes, 0 underruns 0 output errors, 0 collisions, 37 interface resets 0 output buffer failures, 0 output buffers swapped out 54 carrier transitions To reset: BHM# clear counters Bad line, bad hardware Faulty hardware, cable or noise Line interruptions, faulty hardware Layer 1 Troubleshooting – using show interfaces

  25. Layer 1 Troubleshooting – using show interfaces The show interfaces serial command

  26. show controllers serial 0 Router# HD unit 0, idb = 0x1086D4, driver structure at 0x10E568 buffer size 1524 HD unit 0, V.35 DCE cable, clockrate 56000 Layer 1 Troubleshooting – show controllers

  27. Troubleshooting Using show controllers serial The show controllers serial Command

  28. Typical Layer 2 Errors • Improperly configured serial interfaces • Improperly configured Ethernet interfaces • Improper encapsulation set • Improper clock rate settings on serial interfaces • Network interface card (NIC) problems

  29. Troubleshooting Using show cdp neighbors

  30. Troubleshooting Using show cdp neighbors detail

  31. Data-Link layer(up or down) Are keepalives being received? Encapsulation must match at both ends of connection Layer 2 Troubleshooting – show interfaces If the interface is up and the line protocol is down, a Layer 2 problem exists. • Among the possible causes are: • No keepalives ,No clock rate ,Mismatch in encapsulation type BHM# show interface serial 0 Serial0 is up, line protocol is up Hardware is HD64570 Internet address is 172.17.0.2/16 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input 00:00:01, output 00:00:00, output hang never Last clearing of "show interface" counters never < output omitted >

  32. Layer 2 Troubleshooting • If the interface is up and the line protocol is down, a Layer 2 problem exists. • Indicates whether the IOS processes consider the interface usable. • Keepalives are defined as messages sent by one network device to inform another network device that the virtual circuit between the two is still active • If the interface misses three consecutive keepalives, line protocol is down • When the line is down, the protocol is always down    

  33. show interfaces Command

  34. Typical Layer 3 Errors • Routing protocol not enabled • Wrong routing protocol enabled • Incorrect IP addresses • Incorrect subnet masks

  35. Layer 3 Troubleshooting Using Ping

  36. vista# ping SanJose1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 192.168.1.2, timeout is 2 seconds: ..!!! ‘!’ indicate a successful echo ‘.’ indicate the application timed out waiting for an echo Success rate is 60 percent (3/5), round-trip min/avg/max = 32/33/36 ms Ping • Extended ping • provides extra facilities for ping

  37. Troubleshooting Usingtraceroute Command Test on a hop-by-hop basis – Each time is the RTT

  38. Troubleshooting Routing Issues The show ip route Command

  39. Troubleshooting Routing Issues The show ip protocols Command

  40. Introduction to debug Debug syntax

  41. Debug • Used to display dynamic data and events as they occur. • Displays current events of the router, example: • traffic on an interface • error messages generated by nodes on the network • protocol-specific diagnostic packets • Debug commands effect router performance due to high processor overhead. • Debug should be used sparingly to avoid disrupting normal router operation.   

  42. Debug • Debug all • Router# debug all • But don’t use as it can crash the system • Debug output and system messages are sent to the console. • To redirected to a Telnet client: • Router# terminal monitor • To add timestamps to debug messages: • Router(config)# service timestamps debug uptime To Turn off debugging • Router# no debug all • Router# undebug all

  43. Layer 7 Troubleshooting Using Telnet

  44. Summary

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