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QOS HQF. How police and bandwidth percent commands work together in nested policy class?

PARENT_10Mbps policy applied to some interface.

The CHILD policy BULK_CLASS has both "bandwidth percent" and "police" commands applied.

1) Which of these two commands will take effect? Or both commands will work together somehow?

Command "bandwidth percent 5" is 500kbps (bacause of 10Mbits PARENT shaping) and "police 3000000" is 3Mbits.

2) What real speed this class gets in cases of partial and full utilization of 10Mbits?

 

policy-map CHILD
 class VOICE_CLASS
  priority percent 50
 class BUSINESS_TRAFFIC_CLASS
  bandwidth percent 45 
 class BULK_CLASS
  bandwidth percent 5 
  police 3000000 8000 8000 conform-action transmit  exceed-action drop  violate-action drop 
 class class-default
  fair-queue
  random-detect
  
policy-map PARENT_10Mbps
 class class-default
  shape average 10000000
   service-policy CHILD

 

 

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VIP Expert

Re: QOS HQF. How police and bandwidth percent commands work together in nested policy class?

I'm surprised IOS accepted the shown policies. Why? Because 100% has been allocated leaving class-default zero percent. (I recall [?] HQF IOS versions require a minimum of 1% for class-default. [I also recommend all classes have an explicit bandwidth allocation.])

#1 Normally both commands work together. BULK_CLASS will always be "capped" at 3 Mbps due to the policer. If class-default really is only getting a zero percent guarantee, then BULK_CLASS will be dequeued obtaining its 5% relative to the other non-LLQ active classes. So, for example, if only BULK_CLASS and BUSINESS_TRAFFIC_CLASS were only two active classes, and both wanted all the bandwidth, they would split it 45:5 or 9:1, i.e. BUSINESS_TRAFFIC_CLASS would obtain 9 Mbps and BULK_CLASS 1 Mbps (which is within the policer's limit).

#2 Depends on what the other classes are doing. Bandwidth allocations, excluding LLQ, "under-the-covers" really sets relative dequeuing ratios. (LLQ classes always dequeue first, but they have an implicit policer.) Also, prior to HQF, FQ in class-default isn't "limited" just by class bandwidth allocation (it's rather complicated). With HQF, FQ in class-default is supposed to enforce the class bandwidth allocation, but don't know, if bandwidth is undefined, what's supposed to happen.

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9 REPLIES 9
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VIP Mentor

Re: QOS HQF. How police and bandwidth percent commands work together in nested policy class?

Hello

In times of congestion the class- Bulk_Class will receive a minimum of 256kps of BW but could obtain more if the other classes are not being utilized with the police action stating if this class exceeds 3mb then its traffic will be dropped.



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future
Highlighted

Re: QOS HQF. How police and bandwidth percent commands work together in nested policy class?

Thank you for answer.

In times of congestion the class Bulk_Class will receive a minimum of 256kps

You mean 512kbps (5% of 10Mbits) ?

 

Do I correctly understand that these two commands can work together and:

1) Bandwidth percent command guarantees the minimum bandwidth in case of full utilization of channel (10Mbit)

2) Assume that shaping process in some moment of time is ready to give more than 3Mbits to BULK_CLASS (because of channel low utilization by other classes), but configured police command will always drop packets above 3Mbit rate ?

Highlighted
VIP Mentor

Re: QOS HQF. How police and bandwidth percent commands work together in nested policy class?

Hello


@Pavel Komissarov wrote:

Thank you for answer.

In times of congestion the class Bulk_Class will receive a minimum of 256kps

You mean 512kbps (5% of 10Mbits) ?  - <  no it will be 256kps because you have priority LLQ taking 50% of the 10mb

 

Do I correctly understand that these two commands can work together and:

1) Bandwidth percent command guarantees the minimum bandwidth in case of full utilization of channel (10Mbit)  <  yes


2) Assume that shaping process in some moment of time is ready to give more than 3Mbits to BULK_CLASS (because of channel low utilization by other classes), but configured police command will always drop packets above 3Mbit rate ?  <-- correct


 

 



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future
Highlighted

Re: QOS HQF. How police and bandwidth percent commands work together in nested policy class?

Ok. Everything is clear, except:

You mean 512kbps (5% of 10Mbits) ?  - <  no it will be 256kps because you have priority LLQ taking 50% of the 10mb

Don't you by chance confuse bandwidth percent and bandwidth remaining percent commands?

Because from my experience bandwidth percent directly sets percent of bandwidth and doesn't depend on priority percent command parametres from other classes.

Highlighted
VIP Expert

Re: QOS HQF. How police and bandwidth percent commands work together in nested policy class?

"1) Bandwidth percent command guarantees the minimum bandwidth in case of full utilization of channel (10Mbit)"

Yes and no. The guarantee minimum will only match the percentage defined if all 100% has been allocated within the policy and all classes are obtaining, or trying to obtain, bandwidths that meet (or exceed) the defined percentage.

For example,

policy x
class a
bandwidth percent 50
class b
bandwidth percent 50

policy y
class a
bandwidth percent 1
class b
bandwidth percent 1

The above two policies will effectively provide the same results because the bandwidth allocations between classes is 1:1.

#2, as noted in my prior post, yes (i.e. police statement always enforces the defined limit).
Highlighted
VIP Expert

Re: QOS HQF. How police and bandwidth percent commands work together in nested policy class?

I'm surprised IOS accepted the shown policies. Why? Because 100% has been allocated leaving class-default zero percent. (I recall [?] HQF IOS versions require a minimum of 1% for class-default. [I also recommend all classes have an explicit bandwidth allocation.])

#1 Normally both commands work together. BULK_CLASS will always be "capped" at 3 Mbps due to the policer. If class-default really is only getting a zero percent guarantee, then BULK_CLASS will be dequeued obtaining its 5% relative to the other non-LLQ active classes. So, for example, if only BULK_CLASS and BUSINESS_TRAFFIC_CLASS were only two active classes, and both wanted all the bandwidth, they would split it 45:5 or 9:1, i.e. BUSINESS_TRAFFIC_CLASS would obtain 9 Mbps and BULK_CLASS 1 Mbps (which is within the policer's limit).

#2 Depends on what the other classes are doing. Bandwidth allocations, excluding LLQ, "under-the-covers" really sets relative dequeuing ratios. (LLQ classes always dequeue first, but they have an implicit policer.) Also, prior to HQF, FQ in class-default isn't "limited" just by class bandwidth allocation (it's rather complicated). With HQF, FQ in class-default is supposed to enforce the class bandwidth allocation, but don't know, if bandwidth is undefined, what's supposed to happen.

View solution in original post

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Re: QOS HQF. How police and bandwidth percent commands work together in nested policy class?

Thank you for answer.

And about this little correction:

I recall [?] HQF IOS versions require a minimum of 1% for class-default.

Yes, you are right. Cisco CLI declines the command, when I try to allocate all 100% of bandwidth percents beetween several classes, but 99% it accepts.

Highlighted
VIP Expert

Re: QOS HQF. How police and bandwidth percent commands work together in nested policy class?

Then in that case, we might presume class-default obtains 1%. However, if you defined less than 99% for other classes, again, not really sure what class-default obtains without an explicit bandwidth allocation. Whatever it obtains in such cases, by default, may vary between IOS variants.

Otherwise, are your questions answered? Bandwidth allocations, for non-LLQ classes, really define dequeuing weights, and dequeuing is relative between those weights. So, again, between BUSINESS_TRAFFIC_CLASS and BULK_CLASS, they will split bandwidth 45:5 or 9:1. This, though, assumes they want their full allocation or more. If, for example, BUSINESS_TRAFFIC_CLASS was only using 1 Mbps, BULK_CLASS class could have the unused bandwidth, yet if both queues had something in their queues as the same moment, BUSINESS_TRAFFIC_CLASS would more often be selected to be dequeued first.

A LLQ class, like your VOICE_CLASS class, will always dequeue before other non-LLQ classes, assuming it's not dropped due to exceeding its bandwidth allocation. However, usually that bandwidth limit is only active when there's actual congestion. If not, generally the LLQ class can exceed the implicit limit. I.e. you could find, for example, VOICE_CLASS using 90% of the bandwidth.

Highlighted

Re: QOS HQF. How police and bandwidth percent commands work together in nested policy class?

Yes, thank you for detailed answers. Everything is clear for now.