QoS parent and child policies

Question on how does a QoS policy mapped to a sub-interface know what the logical bandwidth is? For example, if I have a parent policy that is shaping traffic at a rate of 1GB on a 10GB link and has a nested policy with bandwidth guarantees for multiple classes how does it know to calculate that the logical bandwidth is 1GB vs 10GB when it’s time to guarantee bandwidth percents?

Hello @vjnetwork

If you don’t configure bandwidth under the parent policy then the interface bandwidth is divided by each class under the parent policy. For example:

class-map match-all CHILD_CLASS
class-map match-all PARENT_CLASS
policy-map CHILD
policy-map PARENT
  shape average 700000000   
   service-policy CHILD

interface GigabitEthernet0/1
 service-policy output PARENT

There is no bandwidth command under the parent policy so the PARENT_CLASS and class-default classes would have a minimum guarantee of 500 Mbit (50% of Gigabit interface). The PARENT_CLASS shapes up to 700 Mbit.

On a 10 Gigabit interface with a 1GB shaper, you should set the bandwidth to 1 GB so the child policy inherits 1GB as the bandwidth.

Does this help?


It does help and thank you.

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