DCB Maps and its AttributesThis topic contains the following sections that describe how to configure a DCB map, apply the configured DCB map to a port, configurePFC without a DCB map, and configure lossless queues.DCB Map: Configuration ProcedureA DCB map consists of PFC and ETS parameters. By default, PFC is not enabled on any 802.1p priority and ETS allocates equal bandwidthto each priority. To configure user-defined PFC and ETS settings, you must create a DCB map. The following is an overview of the stepsinvolved 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 thepriority group traffic should be handled with strict priority scheduling. You can enable PFC on a maximum of two priority queues on aninterface. Enabling PFC for dot1p priorities makes the corresponding port queue lossless. The sum of all allocated bandwidthpercentages in all groups in the DCB map must be 100%. Strict-priority traffic is serviced first. Afterwards, you can configure either thepeak rates or the committed rates. The bandwidth allocated to other priority groups is made available and allocated according to thespecified percentages. If a priority group does not use its allocated bandwidth, the unused bandwidth is made available to other prioritygroups.• 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 tothe 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 dot1ppriorities 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 dot1ppriorities 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 ETSparameters revert to their default values on the interfaces on which the DCB map is applied. By default, PFC is not applied on specific802.1p 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 andequally 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 mapconfiguration. Instead, first create a new DCB map with the desired PFC and ETS settings, and apply the new map to the interfaces tooverride 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, thedefault PFC and ETS parameters are applied on the interfaces. This change may create a DCB mismatch with peer DCB devices andinterrupt network operation.Data Center Bridging: Default ConfigurationBefore 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.Data Center Bridging (DCB) 251
