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

[Patrick Cole]

I have plenty of interfaces where I see the average rate is ~ 100-200mbps
less than the shaper, but still can see up to 5 to 10Mbps of bursty traffic 
bєing dropped at times.  

If you want to try and smooth it out somewhat, consider changing your queueing 
strategy to RED or something that will drop frames early instead of waiting
until the queue is full and performing tail drop.   Depending on your traffic
profile (eg TCP or not), this may or may not help.

Regards,

Patrick

Tue, Mar 21, 2017 at 01:23:05PM +1100, Patrick Cole wrote:

> 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
> > _______________________________________________
> > cisco-nsp mailing list  cisco-nsp at puck.nether.net
> > https://puck.nether.net/mailman/listinfo/cisco-nsp
> > archive at http://puck.nether.net/pipermail/cisco-nsp/
> > 
> 
> -- 
> Patrick Cole <z at wwwires.com>
> Senior Network Specialist
> World Without Wires
> PO Box 869. Palm Beach, QLD, 4221
> Ph:  0410 626 630

-- 
Patrick Cole <z at wwwires.com>
Senior Network Specialist
World Without Wires
PO Box 869. Palm Beach, QLD, 4221
Ph:  0410 626 630