Connectivity Guide
PFC conguration notes
• PFC is supported for 802.1p, dot1p priority trac, from 0 to 7. FCoE trac traditionally uses dot1p priority 3 — iSCSI storage trac
uses dot1p priority 4.
• Congure PFC for ingress trac by using network-qos class and policy maps, see Quality of Service. PFC-enabled trac queues are
treated as lossless queues. Congure the same network-qos policy map on all PFC-enabled ports. Congure required bandwidth for
lossless trac using ETS queuing (output) policies on egress interfaces.
• In a network-qos policy-class map, use commands to generate PFC pause frames for matching class-map priorities:
– Send pause frames for matching class-map trac during congestion using the pause command.
– (Optional) Enter user-dened values for the reserved ingress buer-size of PFC class-map trac, and the thresholds used to send
XOFF and XON pause frames using the pause [buffer-size kilobytes pause-threshold kilobytes resume-
threshold
kilobytes]command.
– Congure the matching dot1p values used to send pause frames using the pfc-cos command.
– (Optional) Set the static and dynamic thresholds that determine the shared buers available for PFC class-map trac queues using
the queue-limit thresh-mode command.
• By default, all ingress trac is handled by the lossy ingress buer. When you enable PFC, dot1p ingress trac competes for shared
buers in the lossless pool instead of the shared lossy pool. The number of lossless queues supported on an interface depends on the
amount of available free memory in the lossy pool.
• Use the priority-flow-control mode on command to enable PFC for FCoE and iSCSI trac; for example, priority 3 and 4.
• Enable DCBX on interfaces to detect and auto-congure PFC/ETS parameters from peers.
• PFC and 802.3x LLFC are disabled by default on an interface. You cannot enable PFC and LLFC at the same time. LLFC ensures lossy
trac in best-eort transmission. Enable PFC to enable guarantee lossless FCoE and iSCSI trac. PFC manages buer congestion by
pausing specied ingress dot1p trac; LLFC pauses all data transmission on an interface. To enable LLFC, use the flowcontrol
[receive | transmit] [on | off] command.
• SYSTEM-QOS mode applies a service policy globally on all interfaces:
– Create and apply a 1-to-1 802.1p-priority-to-trac-class mapping on an interface or all interfaces in INTERFACE or SYSTEM-QOS
mode
– Create and apply a 1-to-1 trac-class-to-queue mapping on an interface or all interfaces in INTERFACE or SYSTEM-QOS mode
The S5148F-ON platform has the following limitations:
• You cannot congure PFC priority 0 as a lossless priority.
• You cannot map multiple priorities to the same queue.
• Whenever you enable LLFC on an interface, Rx PFC frames are honored. Also, whenever you enable PFC on an interface, Rx Pause
frames are honored. Rx Pause statistics in the hardware also includes the Rx PFC frames.
Congure dot1p priority to trac class mapping
Converged data center services
1085