[c-nsp] Ang: ME3600X Output Drops

Wed May 8 17:10:49 EDT 2013

Pshem,
The buffers on ME3600X are 18 MB per ASIC. Basically 18 MB for 24 gig ports and 18 MB for 2x10Gig ports.
The buffers are dynamically allocated using intelligent resource scheduler. There is no reserved buffer and the pool is global. Drops are seen due to microburst since defaults are not able to handle big burst.
With this new enhancement (percent based queue-limit) introduced in 15.3(1)S,  you can eliminate or significantly reduce output drops.
BTW the system allows oversubscription in terms of configuration so you can configure more than one queue as 100% percent assuming not all of them will be congested as the same time.

Best Regards,

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From: Pshem Kowalczyk <pshem.k at gmail.com<mailto:pshem.k at gmail.com>>
Date: Tuesday, May 7, 2013 2:57 PM
To: "cisco-nsp at puck.nether.net<mailto:cisco-nsp at puck.nether.net>" <cisco-nsp at puck.nether.net<mailto:cisco-nsp at puck.nether.net>>
Subject: Re: [c-nsp] Ang: ME3600X Output Drops

Hi All,

I think we have finally got rid of the drops on ME3600X by using the
following config on each EVC:

policy-map PM-CUST-DEFAULT-20M-OUT
description limiting to 20 Mbps
class CM-DUMMY
class class-default
  shape average 20000000
  queue-limit percent 100

The key for us was 'queue-limit percent 100'. With statically defined
queue depth, even with 2MB of buffer per EVC we were getting drops on
4Mb/s flows. I was told that with this sets the buffers to dynamically
allocated as needed.
This is using 15.3(2)S.

kind regards
Pshem

On 21 August 2012 21:32,  <Gustav.Ulander at steria.se<mailto:Gustav.Ulander at steria.se>> wrote:
We have the same problem on our 3600X devices.
Look at bugg CSCua16046
We belive that is the bug that we are encountering. Havent updated software
on the device yet though.

-----cisco-nsp-bounces at puck.nether.net<mailto:-----cisco-nsp-bounces at puck.nether.net> skrev: -----
Till: cisco-nsp at puck.nether.net<mailto:cisco-nsp at puck.nether.net>
Från: "Ivan"
Sänt av: cisco-nsp-bounces at puck.nether.net<mailto:cisco-nsp-bounces at puck.nether.net>
Datum: 2012-08-21 01:49
Ärende: [c-nsp] ME3600X Output Drops

Hi,

I am seeing output drops on a ME3600X interface as shown below

GigabitEthernet0/2 is up, line protocol is up (connected)
   MTU 9216 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
      reliability 255/255, txload 29/255, rxload 2/255
   Encapsulation ARPA, loopback not set
   Keepalive set (10 sec)
   Full-duplex, 1000Mb/s, media type is RJ45
   input flow-control is off, output flow-control is unsupported
   ARP type: ARPA, ARP Timeout 04:00:00
   Last input 6w1d, output never, output hang never
   Last clearing of "show interface" counters 00:12:56
   Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 231
   Queueing strategy: fifo
   Output queue: 0/40 (size/max)
   30 second input rate 10299000 bits/sec, 5463 packets/sec
   30 second output rate 114235000 bits/sec, 12461 packets/sec
      3812300 packets input, 705758638 bytes, 0 no buffer
      Received 776 broadcasts (776 multicasts)
      0 runts, 0 giants, 0 throttles
      0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
      0 watchdog, 776 multicast, 0 pause input
      0 input packets with dribble condition detected
      9103882 packets output, 10291542297 bytes, 0 underruns
      0 output errors, 0 collisions, 0 interface resets
      0 unknown protocol drops
      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

I have read about similar issues on the list:
http://www.gossamer-threads.com/lists/cisco/nsp/157217
https://puck.nether.net/pipermail/cisco-nsp/2012-July/085889.html

1. I have no QoS policies applied to the physical interface or EVCs.
Would increasing the hold queue help?  Is there a recommended value - the
maximum configurable is 240000.  What is the impact on the 44MB of packet
buffer.

2. If the hold queue isn't an option is configuring QoS required to
increase the queue-limit from the default 100us.  Again are there any
recommended values and what impact is there on the available 44MB of
packet buffer.

3. I have found that when applying policies to the EVCs the "show policy
map" output does not have information for the queue-limit as I have seen
when applying polices to the physical interface.  Does this mean that EVCs
will still suffer from output drops?

Thanks

Ivan

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