[c-nsp] cisco buffer misses

[Matthew Huff]

Generally switch qos will hurt rather than help output drops. When you turn on QOS you carve up the output queues into multiple smaller queues. You can tag low priority traffic and shape it out to one of the queues, but even then you will actually end up with more discards, albeit discarding stuff which has a lower interest.

Most likely the problem is data going into the switch, unless you have multicast/broadcast traffic that aggregates into ports that are overloaded. These problems are hard to diagnose since over a 3 minute interval (or 30 seconds if you change the load-interval) the traffic can look smooth and lower bandwidth, but under shorter intervals it can overload the output buffers.



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Matthew Huff             | 1 Manhattanville Rd
Director of Operations   | Purchase, NY 10577
OTA Management LLC       | Phone: 914-460-4039


> -----Original Message-----
> From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Michael Sprouffske
> Sent: Thursday, April 18, 2013 1:47 PM
> To: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] cisco buffer misses
> 
> I'm thinking that some switch qos needs to be put in place to resolve this issue.  What does everyone
> think?  We currently don't have qos running in the switched network.  We only have qos running on the
> routers for the uplinks.
> 
> 
> 
> 
> ________________________________
>  From: Michael Sprouffske <msprouffske at yahoo.com>
> To: "cisco-nsp at puck.nether.net" <cisco-nsp at puck.nether.net>
> Sent: Thursday, April 18, 2013 9:40 AM
> Subject: cisco buffer misses
> 
> 
> 
> Could someone give me some insight as to what is causing the misses?  I'm currently researching this
> on the inter webs.  I also notice an interface with several drops as well.
> 
> 
> 
> 
> model: WS-C3750X-24T-S
> 
> 
> 
> Buffer elements:
>      1061 in free list (500 max allowed)
>      3479036431 hits, 0 misses, 1024 created
> 
> Public buffer pools:
> Small buffers, 104 bytes (total 50, permanent 50, peak 119 @ 7w0d):
>      49 in free list (20 min, 150 max allowed)
>      1712506149 hits, 23 misses, 69 trims, 69 created
>      0 failures (0 no memory)
> Middle buffers, 600 bytes (total 25, permanent 25, peak 85 @ 7w0d):
>      23 in free list (10 min, 150 max allowed)
>      167702 hits, 58 misses, 174 trims, 174 created
>      0 failures (0 no memory)
> Big buffers, 1536 bytes (total 50, permanent 50,
>  peak 119 @ 7w0d):
>      50 in free list (5 min, 150 max allowed)
>      244703400 hits, 39 misses, 117 trims, 117 created
>      0 failures (0 no memory)
> VeryBig buffers, 4520 bytes (total 16, permanent 10, peak 16 @ 7w0d):
>      0 in free list (0 min, 100 max allowed)
>      59 hits, 3 misses, 1429 trims, 1435 created
>      0 failures (0 no memory)
> Large buffers, 5024 bytes (total 0, permanent 0):
>      0 in free list (0 min, 10 max allowed)
>      0 hits, 0 misses, 0 trims, 0 created
>      0 failures (0 no memory)
> Huge buffers, 18024 bytes (total 4, permanent 0, peak 7 @ 7w0d):
>      4 in free list (0 min, 4 max allowed)
>      145363512 hits, 412449 misses, 822729 trims, 822733
>  created
>      0 failures (0 no memory)
> 
> 
> 
> 
> GigabitEthernet1/0/11 is up, line protocol is up (connected)
>   Hardware is Gigabit Ethernet, address is 649e.f3e2.7b8b (bia 649e.f3e2.7b8b)
>   Description: server ports
>   MTU 9000 bytes, BW 100000 Kbit, DLY 100 usec,
>      reliability 255/255, txload 1/255, rxload 1/255
>   Encapsulation ARPA, loopback not set
>   Keepalive set (10 sec)
> 
>  Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX
>   input flow-control is off, output flow-control is unsupported
>   ARP type: ARPA, ARP Timeout 04:00:00
>   Last input 00:00:16, output 00:00:01, output hang never
>   Last clearing of "show interface" counters never
>   Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 54011
>   Queueing strategy: fifo
>   Output queue: 0/40 (size/max)
>   5 minute input rate 0 bits/sec, 0 packets/sec
>   5 minute output rate 49000 bits/sec, 28 packets/sec
>      837676 packets input, 118543994 bytes, 0 no buffer
>      Received 492811 broadcasts (481207 multicasts)
>      0 runts, 0 giants, 0 throttles
>      0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
>      0 watchdog, 481207 multicast, 0 pause input
> 
>  0 input packets with dribble condition detected
>      670450255 packets output, 115399962776 bytes, 0 underruns
>      0 output errors, 0 collisions, 1 interface resets
>      0 babbles, 0 late collision, 0 deferred
>      0 lost carrier, 0 no carrier, 0 PAUSE output
>      0 output buffer failures, 0 output buffers swapped out
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