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QoS bandwidth allocation when there is congestion but no priority traffic

Hi All,

if I have a queuing scheme similar to below and when there is no congestion or realtime traffic would queuing be FIFO and when congestion occurred due to transactional traffic would the transactional be limited to using 16% of the 4M and remaining bandwidth allocated to the other classes or transactional takes majority of bandwidth and other classes limited to their defined percentage


policy-map OUT-01

class realtime

priority 2000

police 2000000 conform-action transmit exceed-action drop

class priority

bandwidth remaining percent 40

random-detect dscp-based

class missioncritical

bandwidth remaining percent 39

random-detect dscp-based

class transactional

bandwidth remaining percent 16

random-detect dscp-based

class general

bandwidth remaining percent 1

random-detect dscp-based

class class-default

bandwidth remaining percent 4

random-detect dscp-based

policy-map OUT-SHAPE

class class-default

shape average 4000000 17000 0


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Generally, "ordinary" CBWFQ bandwidth settings set a guaranteed minimum, they do not limit.  For example, your 16% transaction could use 100%.

Also on most CBWFQ platforms (ASRs being an exception?), "bandwidth" classes containing for bandwidth will split it in the ratios of their bandwidth statement assignments.  For example if your transactional, general and default classes were contending for bandwidth, they would split it 16:4:1.

BTW, your 16% is defined as "remaining", so it doesn't guarantee 16% of the 4 Mbps because you've also defined a LLQ class with 2 Mbps.  I.e. you've "guaranteed" 16% of the remaining 2 Mbps.


Also BTW, unless you're a QoS expert I would recommend you NOT use random-detect.

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