Information About Link Level Flow Control; Link Level Flow Control On Interfaces; Link Level Flow Control On Ports - Cisco Nexus 9000 Series Configuration Manual

Information About Link Level Flow Control

• Enabling link level flow control requires a part of the buffer to be reserved. This reduces the available
• Data Center Bridging Exchange Protocol (DCBX) is not supported.
• Configuration time quanta of the pause frames is not supported.
• On each Ethernet interface, the switch can enable either PFC or LLFC, but not both.
• Only pure CoS-based classification of traffic classes is supported.
• Setting of pause threshold values is restricted.
• Configuring Link Level Flow Control on the interfaces will flap the interfaces which results in a
• When a no-drop QoS group is configured, you must ensure that packets received on ports that do not
• Only a no-drop QoS group is capable of generating link level pause frames.
• Weighted Random Early Detection (WRED) should not be enabled on a no-drop class because it can
• It is recommended to use default buffer sizes for no-drop classes because if the buffer size is specified
• It is recommended to change the LLFC configuration when there is no traffic, otherwise packets already
• Beginning with NX-OS 7.0(3)I1(2), link level flow control and PFC are supported on Cisco Nexus 9300
Information About Link Level Flow Control

Link Level Flow Control on Interfaces

When link level flow control is configured the system changes the interface state to Down if the specified
interface is in UP state and then applies the flow control configuration. After the configuration is successfully
applied to the interface, the system restores the interface to the UP state.

Link Level Flow Control on Ports

During a port shutdown event, the flow-control settings on an interface are retained, however no traffic is
received or transmitted on the link. During a port startup event the flow-control settings are reinstated on to
the hardware.
Cisco Nexus 9000 Series NX-OS Quality of Service Configuration Guide, Release 7.x
132
shared buffer space.
Note When both PFC and LLFC are enabled, LLFC is selected.
momentary traffic loss.
have flow control send-on configured are not classified to a no-drop QoS group.
cause egress queue drops.
through CLI, it will allocate the same buffer size for all ports irrespective of the link speed, and MTU
size.
in the MMU of the system may not get the expected treatment.
Series switches and line cards that contain the ALE (Application Leaf Engine).
Configuring Link Level Flow Control