QoS Shaper and Fractional Circuits

[Patrick McHenry]

Hi,

On a fractional circuit…say 20 Mbps, connected via a gigabit interface it is understood that a shaper should shape the outbound policy-map to match.

What about a 100 Mbps circuit where the gigabit interface connecting to the provider has been configured for 100 full.

Should that be shaped to 100 Mbps as well? Or, by configuring the interface to 100 full are we changing the serialization of the link to behave like a 100 Mbps interface?

Thank you

[Joseph W. Doherty]

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Posting

Should that be shaped to 100 Mbps as well? Or, by configuring the interface to 100 full are we changing the serialization of the link to behave like a 100 Mbps interface?

Often yes, if you physically run at gig with a 100 Mbps CIR.

If your run the link physically at 100 Mbps it will behave exactly like a 100 Mbps interface because that's what you just configured it to be.  (BTW, shapers try to emulate a specific bandwidth, but they don't exactly mimic that bandwidth.)

[Patrick McHenry]

Thanks for the reply Joseph

So it I understand correctly, and I realize we are usually bound to the speed a provider wants us to configure our connecting interfaces, but it would be better to set a gigabit interface to 100 Full than to leave the interface at 1 gig and shape to 100 Mbps?

Thank you

[Joseph W. Doherty]

Personally, in a situation like this, I often chose to run the interface at 100 Mbps.  This because I often also configure QoS, and QoS often seems to work "better" when tied to a physical port bandwidth.

However, shapers do allow you to burst, and depending on how your service provider is enforcing the bandwidth, being able to briefly send/receive at gig might benefit some traffic.

In other words this is a "it depends" kind of answer.