Packet drops on Campus Network .....

Unanswered Question
Dec 30th, 2007

Dear All,

We have a Campus Network of around 250 Nos of L2 Switches and 2 Nos of Core Switches ( 6506 ) with 2 Msfcs in each.

Total 60 Vlans are active on it.

Network is working Ok but some ties there are packets dropping on somw of the switches and Vlan gateways ( HSRP standby IP ). Physical connectivity is oK everywhere. and it self it works well.

Can any body suggest me the reason for the same or the method to trace the reason ?

I am attaching the tech-support of one of the msfc.

I have this problem too.
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pciaccio Mon, 12/31/2007 - 08:50

From your show tech-support you supplied I see all your interface VLANs have input drops. All the counters were never reset so I cannot determine how bad these drops are, however first reset all the counters on your interfaces and see how bad the Input drops are. Next I would determine what interfaces have the most traffic on them. The Input queues are being over-run and so traffic gets dropped when the interface cannot handle the data. All the interfaces are set for FIFO queuing. I would suggest first to increase the input queue size under the interface (input-queue 125 in) This will increase the input queue size to 125. This will decrease the drops, however your overall resolution would be to inplement QOS on your network. This would classify and police the traffic that you deem important... Good Luck..

Dipesh Patel Wed, 01/09/2008 - 02:33

Dear pciaccio,

I have done as per your suggation. But again the same problem occurs.... I m sending you the Tech support after clearing counter and increasing input queue depth.

Check the following Buffer analysis using Cisco output interpreter:




ERROR: This router has dropped 389172 packet(s) (98.78314%) due to a shortage

of 'Huge buffers'.

NOTE: The term 'Failures' in the huge buffers tracks the number of packets that

were dropped due to unsuccessful attempts to allocate a buffer. This can occur

in spite of (or even because of) the router's attempts to create additional free

buffers when their number declines below minimum.

TRY THIS: Use the 'show memory' command to check the amount of free memory.

CAUTION: Care, expertise, and follow-up monitoring are necessary if system buffers

need to be adjusted. Incorrect adjustments can severely affect hardware and network


WARNING: This router has dropped 1819459 packet(s) (0.06633%) due to a shortage

of 'Small buffers'.

WARNING: This router has dropped 681584 packet(s) (0.01844%) due to a shortage

of 'Middle buffers'.

WARNING: This router has dropped 405683 packet(s) (0.33161%) due to a shortage

of 'Big buffers'.

WARNING: This router has dropped 392701 packet(s) (85.46975%) due to a shortage

of 'VeryBig buffers'.

WARNING: This router has dropped 390557 packet(s) (98.40335%) due to a shortage

of 'Large buffers'.

INFO: If new buffers are not available, the packets are not dropped but the next

largest buffer size is used. So these buffer failures can be ignored.

INFO: The buffer counters can be cleared only by reloading the router.

INFO: Interfaces use the 'interface buffer' pools for input and output (I/O).

When there are no more buffers in the interface buffer free list, the router

goes to the public buffer pools as a fallback. Performance is not affected in

case of a fallback. Interface buffers should not be tuned.


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