Ignored packets

Unanswered Question
Aug 11th, 2009

Hello All,

I would like to understand the root cause for ignored packets , I have a 2811 router with 2 FE I'm seeing input erro /ignored packet count increasing on one FE which is connected to the service provider - 30 Mbps Ethernet circuit.

As per cisco doc's this can be possible due to faulty interface or over load , In this case I don't see the traffic to be over loaded so I have tried changing the Router but still I see ignored / input errors increasing very frequently.

Due to this ignored packet count , We are facing performance issue wrt video conferencing , Any suggestions.

I have this problem too.
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kwillacey Wed, 08/12/2009 - 09:00

input errors may indicate duplex or speed mismatches have you verified that they are correct?

kwillacey Wed, 08/12/2009 - 09:19

if ur 'no buffer counter' increases as the document suggests then you may try tuning the buffers if not then TAC is your best option.

vsraghav123 Thu, 08/13/2009 - 01:32

Yes I checked that as well and don't see it to be a buffer leak.

Will 2811 support 30 Mbps link ?? Are these drops due to hardware not supporting the WAN BW ( Though the ignored count are observed when the traffic is less than 5Mbps)

Joseph W. Doherty Thu, 08/13/2009 - 05:02

"Will 2811 support 30 Mbps link ??"

The 2811 is rated at 120 Kpps (CEF), so in theory, it can handle 30 Mbps (duplex), but in practice, you need to allow CPU for other purposes, and occasional non-CEF forwarding. We also want to avoid situations (i.e. proper sizing) where a software based router's CPU is likely to be run full out.

In other words, for 30 Mbps (duplex) I would recommend a more powerful ISR; perhaps a 2851.

BTW, what I suspect the issue is, if data can be sent to your 2811, in bursts more than 30 Mbps, the ignored packets might be happening during such bursts.


Another approach might be to slow you interfaces to 10 Mbps and use QoS to manage the occasional traffic congestion. Yes, you give up some bandwidth, but you then are able to guarantee performance.

vsraghav123 Thu, 08/13/2009 - 05:15

Thanks for your response , On a real time I noticed the traffic on 2811 was around 3-4 Mbps during which I observed the ignored packet.So I'm sure there is no congestion causing this issue.

To isolate the issue probably I may need to swap the link to a upgraded ISR and observe also I don't see any issues apart from this ignored count on the interface so Im assuming there is no problem with service provider.

Joseph W. Doherty Thu, 08/13/2009 - 05:22

3-4 Mbps over what time interval?

What you might need to determine is if there are microbursts, and for these, you'll likely need to snif the wire to see them.


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