Summary

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Proficiency in troubleshooting Cisco routers comes through experience as well as following a defined troubleshooting methodology. In this chapter, you learned to troubleshoot in a systematic manner beginning with Layers 1, 2, and then 3. In addition, you learned that it is often helpful to begin the troubleshooting process closest to where the problem seems to originate. As you gain more experience, you will be able to diagnose the problem based on your knowledge and experience, often allowing you to go right to the heart of the problem and correct it. Table 17-1 reviews those troubleshooting commands referenced in the chapter.

Table 17-1. Troubleshooting Scenarios Command Summary

Command	Purpose
Router# show ip interface brief	Displays a summary of configured IP interfaces
Router# ping	Tests IP connectivity
Router# show frame-relay pvc	Verifies status of the Frame Relay PVC
Router# show frame-relay map	Verifies Frame Relay IP or IPX mappings
Router# show running-config	Verifies that the running configuration file is correct
Router# show ip route	Displays the IP routing table to ensure that the correct routes are being received
Router# show ip eigrp interfaces	Verifies which interfaces are being advertised within a particular EIGRP autonomous system
Router# show isdn status	Verifies ISDN switch type, Layers 1, 2, and 3
Router# show interface interface	Displays detailed interface information
Router# debug dialer packets	Displays dialer packet output showing whether packets are classified as "interesting" or "uninteresting"
Router# undebug all	Turns off all debugging on the router
Router# show version	Displays the current configurations register setting
> o/r 0x2142	Within ROMMON mode, changes the configuration register to a value that bypasses the startup config file
> I	Reinitializes (reboots) the router from ROMMON mode
Router(config)# config-register 0x2102	Changes the configuration register back to the original setting, permitting the router to load the startup config file upon next router reboot

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