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Show Buffers - Cisco 3750

Hi,

I've noticed that my Cat 3750 on the show buffers command is getting as many misses as hits:

Interface buffer pools:

supervisor_cpuq_15_pool buffers, 2040 bytes (total 4, permanent 4):

0 in free list (0 min, 4 max allowed)

6860407 hits, 6860403 misses

I assume this isn't normal and can it be adjusted?

I have an 8 channel Mux plugged into the switch passing data(IP) to a Router. Using a BERT tester I get errors after a few minutes. Eliminate the Cat 3750 and do the test again and I get no errors on the BERT.

Any ideas are appreciated.

Thanks

Wayne

2 REPLIES
Cisco Employee

Re: Show Buffers - Cisco 3750

The "misses" counts is misleading in Cat 3750

platform. There are 16 CPU queues in h/w and each

queue is allocated a fixed number of buffers. If the

fixed h/w allocation is used up, the IOS will try to

back fill from a software buffer pool. The "missed"

count in "show buffers" command is incremented each

time when a packet is received and there is no

buffer in the corresponding software pool. So

increasing misses does not necessarily mean packets

are dropped - it only means that the software buffer

pool is empty either because no software buffers

are allocated for the CPU queue, or all software

buffers are allocated inorder to back fill the

hardware buffers. Packets will be dropped only if

all hardware buffers used up. To determine whether

any CPU bound packets are dropped, you should use

the following 3750 platform command instead of the

generic "show buffers" IOS command.

"show platform port-asic stats drop"

New Member

Re: Show Buffers - Cisco 3750

Many thanks for your reply. Now I understand the output.

Rgds,

Wayne

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