Administrator 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).
Conguring DCB Maps and its Attributes
This topic contains the following sections that describe how to congure a DCB map, apply the congured DCB map to a port,
congure PFC without a DCB map, and congure lossless queues.
DCB Map: Conguration Procedure
A DCB map consists of PFC and ETS parameters. By default, PFC is not enabled on any 802.1p priority and ETS allocates equal
bandwidth to each priority. To congure user-dened PFC and ETS settings, you must create a DCB map.
Step
Task Command Command Mode
1
Enter global conguration mode to create a DCB map or
edit PFC and ETS settings.
dcb-map name
CONFIGURATION
2
Congure the PFC setting (on or o) and the ETS
bandwidth percentage allocated to trac in each priority
group, or whether the priority group trac should be
handled with strict priority scheduling. You can enable PFC
on a maximum of two priority queues on an interface.
Enabling PFC for dot1p priorities makes the corresponding
port queue lossless. The sum of all allocated bandwidth
percentages in all groups in the DCB map must be 100%.
Strict-priority trac is serviced rst. Afterwards,
bandwidth allocated to other priority groups is made
available and allocated according to the specied
priority-group
group_num {bandwidth
percentage | strict-priority} pfc
{on | o}
DCB MAP
Data Center Bridging (DCB)
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