Cisco Systems CCNA 2 9.3 Troubleshooting Router Issues Overview

9.3 Troubleshooting Router Issues Overview

Essential Labs: 9.3.4, 9.3.5, and 9.3.7

Optional Labs: None

Core TIs: All

Optional TIs: none

Course-Level Claim: Students can use the commands incorporated within IOS to analyze

and rectify network problems.

Certification-Level Claim: Students can perform simple WAN troubleshooting.

Hands-on skills: none

The Cisco IOS contains many troubleshooting commands. The show commands are widely

used. The show interfaces command is used to check the status and statistics of the

interfaces. The show interfaces serial command displays the line and data link

protocol status. It also provides information to help diagnose other Layer 1 issues that are not

as easy to determine. These problems include line interruptions, faulty switch, faulty DSU, or

faulty router hardware. Have the students view the results displayed by these commands and

discuss the results to make sure they understand the output. This is an important concept and

valuable tool for troubleshooting.

The show interfaces command is possibly the most important tool to discover Layer 1 and

Layer 2 problems in the router. The first parameter refers to the physical layer. The second

parameter indicates if the IOS processes that control the line protocol consider the interface to

be usable. This is determined by whether keepalives are successfully received. If the interface

misses three consecutive keepalives, the line protocol is marked as down. The show

interfaces serial command should be used after a serial interface is configured to verify

the changes and that the interface is operational.

View these results with the students and discuss the results to make sure they understand the

output. This is an important concept and valuable tool for troubleshooting. The students are

not expected to understand all the fields contained in the show interfaces command

output. This command will be revisited in CCNA 4 and more information will be presented.

CDP advertises device information to its direct neighbors that includes MAC and IP addresses

and outgoing interfaces. The output from the show cdp neighbors command displays

information about directly connected neighbors. This information can be used to debug

connectivity issues. The show cdp neighbor detail command returns specific device

details such as the active interfaces, the port ID, and the device. The version of Cisco IOS that

is used on the remote devices is also shown.