QOS Shaping dropping packets

[matthewk14]

We have a shaping policy which is dropping packets when there is a spike in data, even though the spike is no where near close to the shaping limit.

An example is the shaping policy limits the outgoing flow on  fiber connection to 10000 Kbps.  There is a routing ssh rsync backup which kicks off every so often that only peaks around 2400 Kbps.  Liveaction shows dropped packets everytime this process kicks off.  Once the shaper policy is removed from the outgoing interface, the packet dropping stops.  

Does anyone have any explanation why this is happening?  Is this expected behavior?

[Joseph W. Doherty]

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Posting

It could be normal behavior.  You're probably having short term bursts exceeding your CIR (remember, usually shapers are measuring down at the millisecond level) and when that happens, your shaping queue(s) cannot contain all the packets being shaped.

[Vasilii Mikhailovskii]

Hello.

Could you provide "show policy-map interface <egress interface>" and highlight the class with the drops?

What is the line-speed of the egress interface?

What is the platform you are running (IOS/IOS-XE/XR and release)?

[matthewk14]

Thanks for the response here is the sh policy-map int g0/1.42 interface in question:  As you can see all the qos hierarchical policy-maps have been removed for troubleshooting.  when applied - the drops coincide with the scavenger class, where I have the ssh backups going, but even without the policies, the class-default still drops the packets once the spike begins from the backup traffic.  

As you can see from the policy - the gigabit interface is using shaping to restrict down to match the 10Mb Fiber connection.  

We are running IOS 15.5-3.M2

GigabitEthernet0/1.42

Service-policy output: SHAPER-FIBER-10M

Class-map: class-default (match-any)
11427055 packets, 6783795232 bytes
5 minute offered rate 551000 bps, drop rate 0000 bps
Match: any
Queueing
queue limit 64 packets
(queue depth/total drops/no-buffer drops) 0/17327/0
(pkts output/bytes output) 11409053/6759822540
shape (average) cir 10000000, bc 80000, be 80000
target shape rate 10000000