How to troubleshoot the Cisco router for beginners

This is a guide to help new Cisco router administrators to learn how to troubleshoot their Cisco routers.

Following are the quick troubleshooting guides.

1) ping (Used to check if you can reach the other Cisco router, network equipments or servers)

2) traceroute (You will see a trace of the path where your package is travelling, if any of the network equipment along the path is having issue or being blocked then you will know that the particular equipment is down or faulty, and from there you can fix it and know the root cause)

3) Always have a corporate network diagram with you when you are troubleshooting. This will assist you to check which network or server equipment you should be pinging or tracerouting to. And you can also telnet into the particular router or server to check if there are any interface problems.

4) Next if you suspect that a interface is having issue. Then you can reset the interface with the following commands.

    router#conf t

    router(config)#int s1/0

    router(config-int)#shut

    Count to 10 slowly and then re-enable the interface

    router(config-int)#no shut

    router(config-int)#^Z

    router#

    If you router is up and running then congrates! If not, then proceed to next step

5) Reboot the router with the following command

    router#reload

6) If nothing works then proceed to do the next command to check your interface

    #sho int s1/0

    Now lookout for the input errors

    Overrun,  ignored and abort errors shows that the Cisco router cannot process incoming packets fast enough and is forced to drop some of the packets. You can adjust the Cisco router's  internal buffers but this is difficult to amend correctly. If this happens, call your Cisco support if you have any.

7) Next is the output error, which is the most common in ethernet interface. There are often high collision rate which will effect performance. On a serial line, output errors. IF this happens contact your Cisco support

8) Carrier transitions counts happens when the interface goes up and down. IF you see your Cisco router's serial interface goes up and down then this is a unstable interface. Contact your Cisco suport to check your hardware quickly

How to configure ISP line into Cisco router

router#conf t

router(config)# int <serial interface name>

router(config t)#description ISP Uplink, circuit ID #<circuit ID>, customer #<numbers>

router(config-if)#encapsulation <encapsulation>

router(config-if)ip address <your end of circuit IP address> <netmask>

router(config-if)^Z

After you entered the above commands, your T1 should show a status and line protocol up.

Now try to ping the ISP's side of the T1 line. You should be able to get a response from them.

Next save your work.

router#write memory

Next you will need to configure the Cisco router's ethernet interface.

router#config t

router(config)#int <ehternet interface name>

router(config-if)ip address <IP address for router> <netmask>

router(config-if)^Z

After saving your work, set the default route

router(config)#ip route 0.0.0.0 0.0.0.0 <ISP side of T1 circuit>

Now try to ping any host in the public internet

Done!