Issue with my 2811 router

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Feb 24th, 2009
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I have a router that keeps dropping packets. I did a show tech and noticed its filling up the buffers. A sh proc shows the router today is running between 40-65% today.


I did a sh int Fa0/0

5 minute output rate 533000 bits/sec, 308 packets/sec

17515940 packets input, 2603146576 bytes

Received 3313844 broadcasts, 6 runts, 0 giants, 897 throttles

27825 input errors, 6 CRC, 0 frame, 0 overrun, 27813 ignored

0 watchdog

0 input packets with dribble condition detected

1191392 packets output, 254392010 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

129 unknown protocol drops

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier

0 output buffer failures, 0 output buffers swapped out



I am getting Input errors along with ignores. Very little CRC errors too.


I am a bit confused here on to what is causing this issue.


With the IP Input taking up 30-40% of the proc I imagine its going to be soemthing pegging the router?


I currently am sniffering the port to pull logs.


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Giuseppe Larosa Tue, 02/24/2009 - 12:32
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Hello Donald,

I would check with

sh ip int fas0/0


if CEF and fast switching are enabled because probably these packets are process switched and for this reason there is an high cpu usage.

The ignored are caused by this high load.


Hope to help

Giuseppe




D0nprintup_2 Tue, 02/24/2009 - 12:34
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THats what I was thinking. What is the correct way to resolve it?


shouls I turn off cef? (I did it for alittle bit but i couldnt tell if it made any difference)


Giuseppe Larosa Tue, 02/24/2009 - 12:39
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Hello Donald,

it is rather the opposite if CEF is disabled you should enable it

CEF is the most efficient way to process traffic.


Being the C2811 a software based router if the traffic volume is high you can expect high cpu load also when CEF is enabled.

So also tracing a graphic of link usage can be a way to understand if this is acceptable or the sign of a problem


Hope to help

Giuseppe


D0nprintup_2 Tue, 02/24/2009 - 12:52
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So if this is normal traffic we should upgrade to a bigger router.


Also if this is normal, if its filling the buffers up that could be the issue with the input errors. THe input errors almost match the ignored but that again is related to buffers filling up.


THis is one of our 2 voice routers. From the research I did today, I think I may need to move one of the PRI's to the other router since it looks like all 48 lines are filling on this one.


I know it be easier for me to move it than to call the carrier and get them to change the hunting on those lines

Giuseppe Larosa Tue, 02/24/2009 - 13:06
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Hello Donald,


>> I think I may need to move one of the PRI's to the other router since it looks like all 48 lines are filling on this one.


I agree this can help


Hope to help

Giuseppe


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