1 CCNA 2 v3.1 Module 9

2 Basic Router Troubleshooting CCNA 2, Module 9

333 Router#show ip route Displays the content of the IP routing table Entries for all known networks and subnets Code that indicates how network was learned

444 New Routes can be Added Statically Administrator manually defines routes Routes do not change until administrator manually programs the changes Dynamically Routing protocol exchange routing information Router independently selects the best path Routes change automatically as neighboring routers update each other with new information

555 Static Routing Advantages Lower processor overheads Lower memory overheads No bandwidth utilization Secure operation Predictability Static Routing Disadvantages High maintenance configuration No adaptability to change

666 Dynamic Routing Advantages High degree of adaptability Low maintenance configuration Dynamic Routing Disadvantages Increased Processor overheads Increased memory utilization High bandwidth utilization

777 Gateway of Last Resort (Default Gateway) Used when the router is unable to match a destination network keep routing tables as lean as possible Router can forward packets destined to any Internet host without having to maintain entry for every Internet network Configured by administrator Router(config)#ip default network Or Router(config)#ip route To find out the default route use show ip route

888 Route Source and Destination Path determination occurs at network layer The network layer provides best-effort, end-to- end, packet delivery across interconnected networks Path determination enables a router to Evaluate the available paths to a destination Establish the preferred handling of a packet Uses the IP routing table to do this After the router determines which path to use it takes the packet from one interface and forwards it to another interface (switching)

999 Determine L2 and L3 Address L3 address Used to route the packet from the source network to the destination network L2 address Delivery within a network To get packets from one router to the next The IP source and destination headers do not change

10 Do interactive media lab 9.1.4

11 Determining Route Administrative Distance Administrative distance of the route Used by router to decide the best path to the destination A number that measures the trustworthiness Lower administrative distance is more trustworthy the source Default administrative distance RIP IGRP -100 OSPF – 110 A route is not installed in the routing table if the administrative distance from another source is lower

12 Determining Route Metrics metrics Determine the best route to a destination Measures the desirability of a route The smaller the metric value the better the path RIP – hop count IGRP – bandwidth, delay, (reliability, load) Static values bandwidth and delay don’t change Dynamic values Reliability and load change between interfaces

13 Determining the Route Next Hop When a router receives an incoming packet Router checks the destination address Router attempts to associate this address with a next hop

14 Determine the last Routing Update Show ip route Show ip protocols Show ip rip database

15 Observing Multiple Paths to Destinations Some routing protocols support multiple paths to the same destination Multi-path algorithms permit traffic over multiple lines provide better throughput more reliable IGRP uses load balancing Show ip route

16 Network Testing Start testing network at Layer 1 Work tests up to layer 7

17 Layer 1 Errors Broken cables Disconnected cables Cables connected to the wrong ports Intermittent cable connection Wrong cables used for the task at hand rollovers, crossover and straight-through cables Transceiver problems DCE cable problems DTE cable problems Devices turned off Indicator lights are a useful tool for troubleshooting

18 Layer 2 Errors Improperly configured serial interfaces Improperly configured Ethernet interfaces Improper encapsulation set (HDLC is default for serial interfaces) Improper clockrate settings on serial interfaces Network interface card (NIC) problems

19 Layer 3 Errors Routing protocol not enabled Wrong routing protocol enabled Incorrect IP addresses Incorrect subnet masks

20 Layer 3 troubleshooting using Ping Used to test network connectivity (Layer 3) ping sends a packet to the destination host and then waits for a reply packet from that host (echo protocol) Results help evaluate path-to-host reliability delays over the path whether the host can be reached or is functioning ping uses Internet Control Message Protocol (ICMP) Verifies hardware connection Verifies logical address of the network layer 5 datagrams sent Success = ! Timout =. Extended Ping also

21 Layer 7 troubleshooting using Telnet telnet normally used to connect remote devices gather information run programs Telnet application provides A virtual terminal for connection to routers running TCP/IP Useful to verify that a connection can be made using Telnet A successful Telnet connection indicates that the upper- layer application and the services of lower layers are functioning properly

22 Troubleshooting L1& L1 using show interface Show interfaces displays the status of physical hardware (layer 1) logical software (layer 2) Part 1 is configuration L2 problems Part 2 is hardware Line status L1 problems

23 A high number of interface resets means too many keepalives have been missed. Caused by: Bad line causing carrier transitions Possible hardware problem at the CSU, DSU, or switch Use the clear counters command to reset the counters to zero after an interface problem has been corrected Starting from zero gives a better picture of the current status of the network

24 Keepalives 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, the line protocol is marked as down If the line is down Layer 1 problem Cabling, connectors, equipment powered off or malfunctioning Administratively down - manually disabled in the configuration Interface is up and line protocol is down Layer 2 problem exists No keepalives, No clock rate, Mismatch in encapsulation type When the line is down, the protocol is always down no useable media for the Layer 2 protocol

25 Troubleshooting using Cisco Discovery Protocol CDP advertises device information to its direct neighbors MAC address, IP addresses, outgoing interfaces show cdp neighbors Displays information about directly connected neighbors show cdp neighbors detail displays active interfaces, port ID, device, IOS version For security reasons CDP should be Configured only on links between Cisco devices disabled on user ports or links not locally managed

26 Troubleshooting using traceroute traceroute command is used to Discover the routes that packet take on way to destination Test network layer (Layer 3) on a hop-by-hop basis provide performance benchmarks Traceroute output A list of hops that were successfully reached Every router that the datagram passes through. indicate the specific hop at which the failure is occurring * indicates the packet failed round trip time (RTT) - relative performance of links

27 Troubleshooting using show ip protocols displays values about IP routing protocol information on the entire router which protocols are configured which networks are being advertised which interfaces are sending updates timers, filters, route summarization, route redistribution

28 Troubleshooting using show ip route Displays the contents of the IP routing table entries for all known networks and subnetworks how that information was learned used to verify that the router has a route to that network

29 Troubleshooting using show controllers serial determine the type of cable connected without inspecting the cables Useful for finding a serial interface with No cable The wrong type of cable Defective cable

30 Debug command Produces high processor overhead Should be used isolate problems not monitor normal network operation. By default, the router sends the debug output and system messages to the console. terminal monitor command cam redirect this to a remote terminal Turn off diagnostics no debug all or undebug all The time when debug events occurred timestamps GAD(config)#service timestamps debug uptime