Concept Guide

Hierarchical Scheduling in ETS Output Policies
ETS supports up to three levels of hierarchical scheduling.
For example, you can apply ETS output policies with the following congurations:
Priority group 1 Assigns trac to one priority queue with 20% of the link bandwidth and strict-priority scheduling.
Priority group 2 Assigns trac to one priority queue with 30% of the link bandwidth.
Priority group 3 Assigns trac to two priority queues with 50% of the link bandwidth and strict-priority scheduling.
In this example, the congured ETS bandwidth allocation and scheduler behavior is as follows:
Unused bandwidth
usage:
Normally, if there is no trac or unused bandwidth for a priority group, the bandwidth allocated to the group is
distributed to the other priority groups according to the bandwidth percentage allocated to each group. However,
when three priority groups with dierent bandwidth allocations are used on an interface:
• If priority group 3 has free bandwidth, it is distributed as follows: 20% of the free bandwidth to priority group 1
and 30% of the free bandwidth to priority group 2.
• If priority group 1 or 2 has free bandwidth, (20 + 30)% of the free bandwidth is distributed to priority group 3.
Priority groups 1 and 2 retain whatever free bandwidth remains up to the (20+ 30)%.
Strict-priority
groups:
If two priority groups have strict-priority scheduling, trac assigned from the priority group with the higher
priority-queue number is scheduled rst. However, when three priority groups are used and two groups have strict-
priority scheduling (such as groups 1 and 3 in the example), the strict priority group whose trac is mapped to one
queue takes precedence over the strict priority group whose trac is mapped to two queues.
Therefore, in this example, scheduling trac to priority group 1 (mapped to one strict-priority queue) takes precedence over scheduling
trac to priority group 3 (mapped to two strict-priority queues).
Applying DCB Policies with an ETS Conguration
You can apply a DCB output policy with ETS conguration to all stacked ports in a switch stack or an individual stacked switch. In addition,
you can apply dierent DCB output policies to dierent stack units.
• Apply the specied DCB output policy on all ports of the switch stack or a stacked switch.
CONFIGURATION mode
dcb-policy output stack-unit {all | stack-unit-id} stack-ports all dcb-output-policy-name
Entering this command removes all DCB input policies applied to stacked ports.
Dell Networking Behavior: A dcb-policy output stack-unit all command overwrites any previous dcb-policy output
stack-unit stack-unit-id congurations. Similarly, a dcb-policy output stack-unit stack-unit-id command
overwrites any previous dcb-policy output stack-unit all conguration.
Entering the no dcb-policy output stack-unit all command removes all DCB output policies applied to stacked ports. The
no dcb-policy output stack-unit stack-unit-id command removes only the DCB output policy applied to the specied
switch.
PFC and ETS Conguration Examples
This section contains examples of how to congure and apply DCB input and output policies on an interface.
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Data Center Bridging (DCB)