QoS, CBWFQ , and LLQ

[itninja2010]

I have a question concerning QoS.  If I have a 10M interface and create a policy that allocates 5M to a priority que (LLQ), does that mean that 5M is reserved strictly for that priority que and I only have 5M left for everything else?  Or, is it only allocated when there is congestion and only to whatever is matched by the class-map that is set?  Thanks.

[Joseph W. Doherty]

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Posting

If the interface is congested (queued packets), the LLQ packets, if any, are sent before all other non-LLQ queued packets.  LLQ will also rate-limit its traffic to what's been specified when there's interface congestion.

Some examples for your question:

Interface congested:

You could have 0 Mbps LLQ and up to 10 Mbps for everything else.

You could have 1 Mbps LLQ and up to 9 Mbps for everything else.

You could have 5 Mbps LLQ and up to 5 Mbps for everything else.

Interface not congested:

You could have 6 Mbps LLQ and <= 4 Mbps for everything else.

You could have 9 Mbps LLQ and <= 1 Mbps for everything else.

You could have 10 Mbps LLQ and = 0 Mbps for everything else.

[itninja2010]

So if there was 5M configured in a priority que, it would not be reserved for LLQ use no matter if there were packets using it or not? 

[Joseph W. Doherty]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

IT Ninja wrote:
So if there was 5M configured in a priority que, it would not be reserved for LLQ use no matter if there were packets using it or not?  

Reserved as in guaranteed, yes.  Reserved as unavailable to other traffic when not being used, no.