Users Guide

Port C —> Port B
PFC no-drop queues are congured 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, [trac 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 trac limit. Egress drops are not observed on Port B since trac ow on priorities is mapped to loss less queues.
Port B acting as Ingress
If the trac 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 conguration for queue to dot1p mapping:
Dell(conf)#do show qos dot1p-queue-mapping
Dot1p Priority : 0 1 2 3 4 5 6 7 -> On ingress interfaces[Port A and C] we used
the PFC on priority level.
Queue : 0 0 0 1 2 3 3 3 -> On Egress interface[Port B] we used no-drop
queues.
Lossless trac egresses out the no-drop queues. Ingress 802.1p trac from PFC-enabled peers is automatically mapped to the no-
drop egress queues.
When conguring lossless queues on a port interface, consider the following points:
• By default, no lossless queues are congured on a port.
• A limit of two lossless queues is supported on a port. If the number of lossless queues congured exceeds the maximum
supported limit per port (two), an error message is displayed. Recongure the value to a smaller number of queues.
• If you congure lossless queues on an interface that already has a DCB map with PFC enabled (pfc on), an error message is
displayed.
Step
Task Command Command Mode
1 Enter INTERFACE Conguration mode.
interface
{tengigabitEthernet slot/
port |
fortygigabitEthernet slot/
port}
CONFIGURATION
2
Open a DCB map and enter DCB map conguration
mode.
dcb-map name
INTERFACE
3
Disable PFC.
no pfc mode on
DCB MAP
4
Return to interface conguration mode.
exit
DCB MAP
5
Apply the DCB map, created to disable the PFC
operation, on the interface
dcb-map {name | default}
INTERFACE
6
Congure the port queues that still function as no-drop
queues for lossless trac. For the dot1p-queue
assignments.
The maximum number of lossless queues globally
supported on a port is 2.
You cannot congure PFC no-drop queues on an
interface on which a DCB map with PFC enabled has
pfc no-drop
queuesqueue-range
INTERFACE
252
Data Center Bridging (DCB)