Reference Guide

PFC conguration notes
• PFC is supported for 802.1p priority trac (dot1p 0 to 7). FCoE trac traditionally uses dot1p priority 3 — iSCSI storage trac uses
dot1p priority 4.
• Congure PFC for ingress trac by using network-qos class and policy maps (see Quality of Service). The queues used for PFC-
enabled trac are treated as lossless queues. Congure the same network-qos policy map on all PFC-enabled ports. Congure required
bandwidth for lossless trac 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 trac during congestion (pause command).
– (Optional) Enter user-dened values for the reserved ingress buer-size of PFC class-map trac, and the thresholds used to send
XOFF and XON pause frames (pause [buffer-size kilobytes pause-threshold kilobytes resume-
threshold
kilobytes]command).
– Congure the matching dot1p values used to send pause frames (pfc-cos command).
– (Optional) Set the static and dynamic thresholds that determine the shared buers available for PFC class-map trac queues
(queue-limit thresh-mode command).
• By default, all ingress trac is handled by the lossy ingress buer. When you enable PFC, dot1p ingress trac competes for shared
buers 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 trac (example, priority 3 and 4).
• Enable DCBX on interfaces to detect and auto-congure PFC/ETS parameters from peers.
• PFC and 802.3x link-level ow control (LLFC) are disabled by default on an interface. You cannot enable PFC and LLFC at the same
time. LLFC ensures lossy trac in best-eort transmission. Enable PFC to enable guarantee lossless FCoE and iSCSI trac. PFC
manages buer congestion by pausing specied ingress dot1p trac; LLFC pauses all data transmission on an interface. To enable
LLFC, enter 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-trac-class mapping on an interface or all interfaces in INTERFACE or SYSTEM-QOS
mode
– Create and apply a 1-to-1 trac-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 congure PFC priority 0 as a lossless priority.
• You cannot map multiple priorities to same queue.
• Whenever LLFC is enabled on an interface, Rx PFC frames are honored. Also, whenever PFC is enabled on an interface, Rx Pause
frames are honored. With respect to statistics, Rx Pause statistics in the hardware includes the Rx PFC frames too.
Congure dot1p priority to trac class mapping
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Converged data center services