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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.
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. The following is an
overview of the steps involved in configuring DCB.
● Enter global configuration mode to create a DCB map or edit PFC and ETS settings.
● 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 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 traffic is serviced
first. Afterwards, you can configure either the peak rates or the committed rates. The bandwidth allocated to other priority
groups is made available and allocated according to the specified percentages. If a priority group does not use its allocated
bandwidth, the unused bandwidth is made available to other priority groups.
● Repeat the above procedure to configure PFC and ETS traffic handling for each priority group
● Specify the dot1p priority-to-priority group mapping for each priority. The priority group range is from 0 to 7. All priorities
that map to the same queue must be in the same priority group.
Leave a space between each priority group number. For example: priority-pgid 0 0 0 1 2 4 4 4 in which priority group 0
maps to dot1p priorities 0, 1, and 2; priority group 1 maps to dot1p priority 3; priority group 2 maps to dot1p priority 4; priority
group 4 maps to dot1p priorities 5, 6, and 7.
Important Points to Remember
● If you remove a dot1p priority-to-priority group mapping from a DCB map (no priority pgid command), the PFC and
ETS parameters revert to their default values on the interfaces on which the DCB map is applied. By default, PFC is not
applied on specific 802.1p priorities; ETS assigns equal bandwidth to each 802.1p priority.
As a result, PFC and lossless port queues are disabled on 802.1p priorities, and all priorities are mapped to the same priority
queue and equally share the port bandwidth.
● To change the ETS bandwidth allocation configured for a priority group in a DCB map, do not modify the existing DCB map
configuration. Instead, first create a new DCB map with the desired PFC and ETS settings, and apply the new map to the
interfaces to override the previous DCB map settings. Then, delete the original dot1p priority-priority group mapping.
If you delete the dot1p priority-priority group mapping (no priority pgid command) before you apply the new DCB
map, the default PFC and ETS parameters are applied on the interfaces. This change may create a DCB mismatch with peer
DCB devices and interrupt network operation.
Data Center Bridging: Default Configuration
Before you configure PFC and ETS on a switch see the priority group setting taken into account the following default settings:
DCB is enabled.
PFC and ETS are globally enabled by default.
The default dot1p priority-queue assignments are applied as follows:
DellEMC(conf)#do show qos dot1p-queue-mapping
Dot1p Priority : 0 1 2 3 4 5 6 7
Queue : 0 0 0 1 2 3 3 3
DellEMC(conf)#
PFC is not applied on specific dot1p priorities.
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Data Center Bridging (DCB)