Rate limit and max burst size

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Hello everyone,
We have a WAN circuit that is 100 MB "best effort" (ie not real time or priority) by our provider. We're seeing dropped packets on the WAN interface on our core stack. I opened a case with our provider and they are saying that we are exceeding our policers.  That our traffic isn't being shaped correctly and we are sending them data "too fast"  They said our burst rate by their calculation should be set to 1,280 kb for our circuit.

So I was trying to see if this would be the proper syntax? 

conf port 4:1 rate-limit egress 95 Mbps max-burst-size 1280 Kb

Thinking that the egress should be 95% of the pipe of 100 MB and the burst size what they recommended.

Does that look okay?

Thanks,
Sarah
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Sarah Seidl

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Posted 3 years ago

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EtherMAN, Embassador

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what is your CIR or guaranteed bandwidth.... that is what you need to set as your limiter I would think.  Is the hand off to this carrier 100 mbs or a 1000 mbs ? 
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Sarah Seidl

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100 MB for the guaranteed bandwidth (they said we were overutilizting that), the hand off is 100 MB as well
Thank you
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EtherMAN, Embassador

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Hmmm if both sides if this WAN service is 100 Mbs and both of your WAN ports are 100 Mbs do you see that interface hitting 100 % utilization?  If this is an XOS switch you can look at show port congestion to see if counters are indeed going up then for sure you are over running the interface.  If this is a WAN service where you have multiple services I think I would approach this at a higher layer and try to set some limits or controls on traffic you can afford to drop or buffer vs traffic you must deliver.  If you just set a layer 2 limit it will not be friendly and may make things worse.  If you are not hitting the 100% or don't see any congestion on the WAN port then you may not be getting what you are paying for.. 
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Sarah Seidl

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Thanks again for the reply.  So I am indeed seeing dropped packets on the port that connects to the service providers equipment from our extreme switch (xos).  This made me open a ticket with them to check things out.
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Stephen Williams, Employee

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If, you check "show port utilization" it's only going to give you an average over 5 seconds.  If the traffic is bursty it will not always show high utilization.  Port congestion like EtherMAN suggested is a great indicator of an over utilized port for egress.
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Sarah Seidl

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Thanks for the added info.  I'll keep an eye on utilization too.  And am definitely seeing dropped packets (sh port congestion) incrementing.