Input drops

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Jul 6th, 2007
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We have two core switches on a lan, they both have a gbit wan connection to the wan cloud.

the strange thing is that one switch shows input drops without ever seeming to have a queue, the other switch has no input drops.

Input queue: 0/75/981068/0 (size/max/drops/flushes); Total output drops: 0

The interfaces are routed interfaces on a Cisco 6509-E with sup-720B.

The line card is a WS-X6724-SFP.

Any thoughts ?

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cbeswick Fri, 07/06/2007 - 03:02
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Hi There,

We experienced the same problems on layer 2 trunk links between access layer switches (2950) and Cat 6500s with Sup720.

In the end it turned out to be an issue with the trunk links no trunking VLAN 1. We had to put VLAN 1 back on all trunk links for the interface queue drops to stop.

When we looked at the packet captures the actual issue appeared to be related to ethernet control messages (keepalives). The Cisco 2950's would send these across the trunk link irrelevant of VLAN 1 being on the trunk, but the 6500's would drop the frame if VLAN 1 wasn't on the trunk.

Hope this helps.

xcz504d1114 Fri, 07/06/2007 - 05:30
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Are you using tunnels to the WAN?

jos-sanchez Fri, 07/06/2007 - 05:40
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What is the output for 'sh ip traffic' in IP statistics, in 'bad hop counts' and in 'encapsulation failed' fields ? Are these counters increasing ?


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