Users Guide
NOTE: You cannot enable PFC and link-level ow control at the same time on an
interface.
Conguring Lossless Queues
DCB also supports the manual conguration of lossless queues on an interface when PFC mode is turned o.
Prerequisite: A DCB with PFC conguration is applied to the interface with the following conditions:
• PFC mode is o (no pfc mode on).
•
No PFC priority classes are congured (no pfc priority priority-range).
Example:
Port A —> Port B
Port C —> Port B
PFC no-drop queues are congured for queues 3, 4 on Port B. PFC capability is enabled on priorities 3, 4 on PORT A and C.
Port B acting as Egress
During the congestion, [trac 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 trac limit. Egress drops are not observed on Port B since trac ow on priorities is mapped to loss less queues.
Port B acting as Ingress
If the trac 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 conguration for queue to dot1p mapping:
The conguration of no-drop queues provides exibility for ports on which PFC is not needed but lossless trac should egress from the
interface.
Lossless trac egresses out the no-drop queues. Ingress dot1p trac from PFC-enabled interfaces is automatically mapped to the no-drop
egress queues.
1 Enter INTERFACE Conguration mode.
CONFIGURATION mode
interface type slot/port
2 Congure the port queues that will still function as no-drop queues for lossless trac.
INTERFACE mode
pfc no-drop queues queue-range
For the dot1p-queue assignments, refer to the dot1p Priority-Queue Assignment table.
The maximum number of lossless queues globally supported on the switch is two.
The default: No lossless queues are congured.
3 Congure to drop the unknown unicast packets ooding on lossless priorities.
CONFIGURATION mode
pfc-nodrop-priority l2-dlf drop
4 View the packets drop count corresponding to the priority.
EXEC mode
EXEC Privilege mode
232
Data Center Bridging (DCB)