Reference Guide

Priority group 1 Assigns traffic to one priority queue with 20% of the link bandwidth and strict-
priority scheduling.
Priority group 2 Assigns traffic to one priority queue with 30% of the link bandwidth.
Priority group 3 Assigns traffic to two priority queues with 50% of the link bandwidth and strict-
priority scheduling.
In this example, the configured ETS bandwidth allocation and scheduler behavior is as follows:
Unused
bandwidth
usage:
Normally, if there is no traffic 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 different 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, traffic assigned from the
priority group with the higher priority-queue number is scheduled first. 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 traffic is
mapped to one queue takes precedence over the strict priority group whose traffic
is mapped to two queues.
Therefore, in this example, scheduling traffic to priority group 1 (mapped to one strict-priority queue)
takes precedence over scheduling traffic to priority group 3 (mapped to two strict-priority queues).
Configuring DCB Maps and its Attributes
This topic contains the following sections that describe how to configure a DCB map, apply the
configured DCB map to a port, configure PFC without a DCB map, and configure lossless queues. This
functionality is supported on the S4820T platform.
DCB Map: Configuration 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 configure user-defined PFC and ETS settings, you
must create a DCB map.
Step Task Command Command Mode
1
Enter global configuration mode to create a
DCB map or edit PFC and ETS settings.
dcb-map name
CONFIGURATION
2
Configure the PFC setting (on or off) and the
ETS bandwidth percentage allocated to traffic
in each priority group, or whether the priority
group traffic should be handled with strict
priority-group
group_num {bandwidth
percentage | strict-
priority} pfc {on | off}
DCB MAP
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Data Center Bridging (DCB)