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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.
Dell Networking OS Behavior: As soon as you apply a DCB policy with PFC enabled on an interface,
DCBx starts exchanging information with PFC-enabled peers. The IEEE802.1Qbb, CEE, and CIN versions
of PFC Type, Length, Value (TLV) are supported. DCBx also validates PFC configurations that are received
in TLVs from peer devices.
NOTE: You cannot enable PFC and link-level flow control at the same time on an interface.
Configuring Lossless Queues
DCB also supports the manual configuration of lossless queues on an interface when PFC mode is turned
off.
Prerequisite: A DCB with PFC configuration is applied to the interface with the following conditions:
• PFC mode is off (no pfc mode on).
• No PFC priority classes are configured (no pfc priority priority-range).
Example:
Port A —> Port B
Port C —> Port B
PFC no-drop queues are configured for queues 1, 2 on Port B. PFC capability is enabled on priorities 3, 4
on PORT A and C.
Port B acting as Egress
During the congestion, [traffic pump on priorities 3 and 4 from PORT A and PORT C is at full line rate],
PORT A and C send out the PFCs to rate the traffic limit. Egress drops are not observed on Port B since
traffic flow on priorities is mapped to loss less queues.
Port B acting as Ingress
If the traffic congestion is on PORT B , Egress DROP is on PORT A or C, as the PFC is not enabled on
PORT B.
Refer the following configuration for queue to dot1p mapping:
Dell(conf)#do show qos dot1p-queue-mapping
Dot1p Priority : 0 1 2 3 4 5 6 7
Queue : 2 0 1 3 4 5 6 7
Dell(conf)#
The configuration of no-drop queues provides flexibility for ports on which PFC is not needed but
lossless traffic should egress from the interface.
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Data Center Bridging (DCB)