Prerequisites For Priority Flow Control; Guidelines And Limitations For Priority Flow Control - Cisco Nexus 9000 Series Configuration Manual
Nx-os quality of service configuration, release 7.x
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Prerequisites for Priority Flow Control
PFC asks the peer to stop sending frames of a particular CoS value by sending a pause frame to a well-known
multicast address. This pause frame is a one-hop frame that is not forwarded when received by the peer. When
the congestion is mitigated, PFC can request the peer to restart transmitting frames.
Note
Cisco Nexus 9000 Series switches support the transport of RDMA over Converged Ethernet (RoCE) v1 and
v2 protocols.
Prerequisites for Priority Flow Control
PFC has the following prerequisites:
• You must be familiar with using modular QoS CLI.
• You are logged on to the device.
Guidelines and Limitations for Priority Flow Control
PFC has the following configuration guidelines and limitations:
• PFC is not supported on the Cisco Nexus 9508 switch (NX-OS 7.0(3)F3(3).
• The show commands with the internal keyword are not supported.
• Adding pause buffer size threshold configuration is optional for cable lengths that are less than 100
• Input queuing policy maps cannot have pause buffer and priority/bandwidth together.
• For cable lengths that are greater than 100m, the pause buffer size threshold configuration is mandatory
• If PFC is enabled on a port or a port channel, it does not cause a port flap.
• PFC configuration enables PFC in both the send (Tx) and receive (Rx) direction.
• Configuration time quanta of the pause frames is not supported.
• You can configure a PFC watchdog interval to detect whether packets in a no-drop queue are being
• The configuration does not support pausing selected streams that are mapped to a particular traffic-class
Cisco Nexus 9000 Series NX-OS Quality of Service Configuration Guide, Release 7.x
150
meters and it need not be configured.
and it is required as part of the QoS policy configuration.
drained within a specified time period. When the time period is exceeded, all outgoing packets are dropped
on interfaces that match the PFC queue that is not being drained. Beginning with Cisco NX-OS Release
7.0(3)I4(2), this feature is supported only for Cisco Nexus 9200 Series switches, Cisco Nexus
93108TC-EX, and 93180YC-EX switches, and Cisco Nexus 9508 switches with the X9732C-EX line
cards.
Beginning with Cisco NX-OS Release 7.0(3)I4(5), this feature is supported on Cisco Nexus 9508 switches
with N9K-X9636PQ line cards and Cisco Nexus 3164Q switches.
queue. All flows that are mapped to the class are treated as no-drop. It blocks out scheduling for the
entire queue, which pauses traffic for all the streams in the queue. To achieve lossless service for a
no-drop class, Cisco recommends that you have only the no-drop class traffic on the queue.
Configuring Priority Flow Control
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