lamav Mon, 01/26/2009 - 09:42

Clear the log on your router as well as the counters on the serial interface and then start monitoring from scratch.

The output of a 'show interfaces ' gives a wealth of information regarding packets being dropped, congestion, errors, etc.



Giuseppe Larosa Mon, 01/26/2009 - 09:56

Hello Cisco_Lite,

just to add to Victor's note if you install a tool like MRTG you can read the SNMP MIBs that are associated to all counters that are in the show int type x/y

You can then graph some of them (some selection is needed) on a web page and you can see the trends in output drops and so on.

for MRTG see

This allows to implement several monitoring web pages that are dynamically updated by MRTG and it is very handy.

Hope to help


cisco_lite Mon, 01/26/2009 - 10:24

Thanks. But how can I identify whether the problem is with the link provided by ISP or with the packet corruption/router interface hardware problem.

I am interested in knowing when to escalate to ISP and when not.

Would Cisco NAM module help in this regard instead of MRTG.

Giuseppe Larosa Mon, 01/26/2009 - 11:40

Hello Cisco_Lite,

NAM is a powerful protocol analyzer but it works by receiving a copy of frames to be monitored

(think of a sort of SPAN/monitor session to network module)

this can be useful to demonstrate that packets are going through your C6500 chassis but not to troubleshoot a physical link to the ISP.

for a detailed analysis the sh int type x/y is the right tool

you need to be aware of the meaning of the different fields.

However, if you see input errors of type ignored overrun and output drops this can be caused by your router.

CRCs can mean the link is not good at layer1


table 14 for the meaning of the fields in

sh interface ethernet

Hope to help


Mohamed Sobair Mon, 01/26/2009 - 10:46


a possible way is to have (Rommon) Remote managment configured on a router. Rommon is a Cisco IOS Service classified as follows:

1- Alarms.

2- Event.

The Alarm action occurs on a defined liftime threshhold.

The Event occurs based On the alarm which should be send to NMS system.




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