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Webcast-Catalyst9k
New Member

CBWFQ and Priority Q Scheduling with IOS

All,

I have a question in regards to scheduling in QoS.

I have below 2 priority queues (both pri quese go into one queue we beleive), and 3 CBWFQs.

The qestion is, how are these queus scheduled. I know that priority Qs will be emtied before moving onto the CBWFQ.

On the CBWFQ side, how are these scheduled, in a round-robin way? or is the amount of time they get serviced increased, the bigger the bandwidth statement is configured (Like custom-queuing and bigger queue configured in terms of bytes equates to more time being scheduled to empty the queue before moving onto the next queue)

policy-map carrier_cos

class carrier_EF

priority

police 1605000 8000 8000 conform-action transmit exceed-action drop

class carrier_AF4

priority

police 1530000 71500 71500 conform-action transmit exceed-action drop

class carrier_AF1

bandwidth 6120

class carrier_bulk

bandwidth 5480

class class-default

bandwidth 15265

Sounds to me like CBQFQ is a mixture of priority-queueing and custom-queuing combined.

Many kind regards for you help with this question.

Ken

2 REPLIES
Silver

Re: CBWFQ and Priority Q Scheduling with IOS

CBWFQ i think uses the BW. Say you have 3 BWs A,B,C so time for Queue would be A/(A+B+C). So more traffic can be put in A. SO it is definitely customised but i dont think it has any priority Queuing as it doesnt give you assured forwarding.

New Member

Re: CBWFQ and Priority Q Scheduling with IOS

Thx for that.

So, if I have a 1M/bit cct and have CBWFQ running.

CBWFQ 1 = Bandwdith 600

CBWFQ 2 = Bandwdith 200

CBWFQ 3 = Bandwdith 200 (class class-default)

assume interface is congested. How does the scheduler work?

Is it, within a time period, (let say 1second) it will spend 600ms servicing Q1, then move onto Q2 and spend 200ms on that queue before moving onto Q3 where it will spend a 200MS servicing that Queue and then go back to Q1?

Correct me if Im wrong, but is that the same as Custom Qeueing?

1 Second is a long time so what timer interval is used.

Remember is a 1M/bps circuit.

Kindest regards, and many thx.

Ken

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