Reference Guide

PFC configuration notes
● PFC is supported for 802.1p priority traffic (dot1p 0 to 7). FCoE traffic traditionally uses dot1p priority 3 — iSCSI storage
traffic uses dot1p priority 4.
● Configure PFC for ingress traffic by using network-qos class and policy maps (see Quality of Service). The queues used for
PFC-enabled traffic are treated as lossless queues. Configure the same network-qos policy map on all PFC-enabled ports.
Configure required bandwidth for lossless traffic 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 traffic during congestion (pause command).
○ (Optional) Enter user-defined values for the reserved ingress buffer-size of PFC class-map traffic, and the thresholds
used to send XOFF and XON pause frames (pause [buffer-size kilobytes pause-threshold kilobytes
resume-threshold kilobytes]command).
○ Configure the matching dot1p values used to send pause frames (pfc-cos command).
○ (Optional) Set the static and dynamic thresholds that determine the shared buffers available for PFC class-map traffic
queues (queue-limit thresh-mode command).
● By default, all ingress traffic is handled by the lossy ingress buffer. When you enable PFC, dot1p ingress traffic competes for
shared buffers 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 traffic (example, priority 3
and 4).
● Enable DCBX on interfaces to detect and auto-configure PFC/ETS parameters from peers.
●
PFC and 802.3x link-level flow control (LLFC) are disabled by default on an interface. You cannot enable PFC and LLFC at
the same time. LLFC ensures lossy traffic in best-effort transmission. Enable PFC to enable guarantee lossless FCoE and
iSCSI traffic. PFC manages buffer congestion by pausing specified ingress dot1p traffic; 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-traffic-class mapping on an interface or all interfaces in INTERFACE or
SYSTEM-QOS mode
○ Create and apply a 1-to-1 traffic-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 configure 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.
Configure dot1p priority to traffic class mapping
Decide if you want to use the default 802.1p priority-to-traffic class (qos-group) mapping or configure a new map. By default,
the qos class-trust class map is applied to ingress traffic. The class-trust class instructs OS10 interfaces to honor dot1p or
DSCP traffic.
Dot1p Priority : 0 1 2 3 4 5 6 7
Traffic Class : 1 0 2 3 4 5 6 7
● Apply the default trust map specifying that dot1p values are trusted in SYSTEM-QOS or INTERFACE mode.
trust-map dot1p default
Configure a non-default dot1p-priority-to-traffic class mapping
1. Configure a trust map of dot1p traffic classes in CONFIGURATION mode. A trust map does not modify ingress dot1p values
in output flows.
Assign a qos-group to trusted dot1p values in TRUST mode using 1-to-1 mappings. Dot1p priorities are 0-7. For a PFC
traffic class, map only one dot1p value to a qos-group number; for Broadcom-based NPU platforms, the qos-group
number and the dot1p value must be the same. A qos-group number is used only internally to classify ingress traffic
classes.
trust dot1p-map dot1p-map-name
qos-group {0-7} dot1p {0-7}
exit
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