[c-nsp] Cisco ASR Shaping (Very Basic QoS) - Output Drops

[Patrick Cole]

Troy,

Chances are you're dealing with traffic microbursts.  This is alwayas likely to
happen on sub-rate services.  The drop rate there is only 88kbps, that's not very high.

Patrick

Tue, Mar 21, 2017 at 01:11:11PM +1100, Troy Boutso wrote:


> Hey
> 
> I look after global MPLS network which consists of multiple sub-line rate -
> Layer 2 circuits. Meaning I usually get a 1Gbps ethernet hand-off. But the
> services are usually configured by the provider as 200Mbps or 300Mbps point
> to point circuits. All my circuits terminate on Cisco ASR1000 Series
> routers. Specifically the Cisco ASR1001X routers.
> 
> Currently running: Version 03.15.02.S - Standard Support Release
> 
> 
> In terms of capacity we are usually pretty good. We never tend to go over
> 50% utilization (average), though of coarse there are always bursty periods
> which could use all available bandwidth for very short periods of time.
> 
> What I have done in the past (whilst working for smaller service providers)
> is to apply a very basic Shaping policy on all these sub-line rate links to
> "smooth" out any bursty traffic. I've never really given this a second
> thought. It seems to work fine.
> 
> However lately I've been noticing extended periods where the drop rate is
> rather high. Usually I notice it for a few seconds. Then it stops. But I'm
> noticing it alot more and it is failry constant.
> 
> The overall traffic demand hasn't increased, so not sure what could be
> causing this all of a sudden. Perhaps a new application on the network is
> more "Bursty".
> 
> 
> Here is the output of show policy-map int (sometimes the drop rate is
> 1Mbps) - That is high!
> 
> *sh policy-map int Gi0/0/1 *
> * GigabitEthernet0/0/1 *
> 
> *  Service-policy output: SHAPE198MBPS*
> 
> *    Class-map: class-default (match-any)  *
> *      226356713752 packets, 130403313955357 bytes*
> *      30 second offered rate 101473000 bps, drop rate 88000 bps*
> *      Match: any *
> *      Queueing*
> *      queue limit 512 packets*
> *      (queue depth/total drops/no-buffer drops) 0/43866538/0*
> *      (pkts output/bytes output) 226208256438/130353031064610*
> *      shape (average) cir 198000000, bc 792000, be 792000*
> *      target shape rate 198000000*
> 
> 
> 
> Here is the basic config. Yes very basic.
> 
> *!*
> *policy-map SHAPE198MBPS*
> * class class-default*
> *  shape average 198000000   *
> *  queue-limit 512 packets*
> *!*
> *policy-map SHAPE290MBPS*
> * class class-default*
> *  shape average 290000000   *
> *  queue-limit 512 packets*
> *!*
> 
> 
> *!*
> *interface gi0/0/1*
> * service-policy output SHAPE198MBPS*
> *!*
> 
> 
> 
> 
> Is there anything I can do to make this more effective? Am I overlooking
> something simple?
> I do not want to implement anything too elaborate. My goal is to not
> calssify all the different traffic types in the network and allocate BW. I
> can address performance elsewhere.
> 
> I want to make sure I shape the entire link to the desired rate with
> minimal drops. Should I increase something?
> 
> Thanks you very much in advance.
> 
> Troy
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-- 
Patrick Cole <z at wwwires.com>
Senior Network Specialist
World Without Wires
PO Box 869. Palm Beach, QLD, 4221
Ph:  0410 626 630