enable flow-control ports

enable flow-control [tx-pause {priority priority} | rx-pause {qosprofile qosprofile}] ports [all | port_list]


Enables flow control or priority flow control (PFC) on the specified ports.

Syntax Description


Specifies transmit pause frames.


Specifies all priorities or single priorities--dot1p priority for tagged packets and internal priority for untagged packets. Used with priority flow control only.


Specifies received pause frames.


Specifies a QoS profile (“qp1” “qp2” “qp3” “qp4” “qp5” “qp6” “qp7” “qp8”) to pause for priority flow control packet reception. Used with priority flow control only.


Specifies all ports or slots.


Specifies one or more ports or slots and ports.



Usage Guidelines

With autonegotiation enabled, the Summit family switches and the BlackDiamond 8800 series switches advertise the ability to support pause frames. This includes receiving, reacting to (stopping transmission), and transmitting pause frames. However, the switch does not actually transmit pause frames unless it is configured to do so.

IEEE 802.3x-Flow Control

IEEE 802.3x flow control provides the ability to configure different modes in the default behaviors.

Use this command to configure the switch to transmit link-layer pause frames when congestion is detected. This stops all traffic on the configured port when there is buffer congestion for any traffic type. Use it also to configure the switch to return to the default behavior of processing received pause frames.

To enable TX flow-control, RX flow-control must first be enabled. If you attempt to enable TX flow-control with RX flow-control disabled, an error message is displayed.

IEEE 802.1Qbb-Priority Flow Control

IEEE 802.1Qbb priority flow control provides the ability to configure the switch to transmit link-layer pause frames to stop only a portion of the traffic when congestion is detected.

When IEEE 802.1Qbb priority flow control is enabled on a port, IEEE 802.3x pause functionality is no longer available on that port.

Priority is established for reception of PFC packets with a QoS profile value on the ExtremeXOS switch and for transmission with a priority value added to the PFC packet.
  • QoS profile—Ingress traffic is associated with a QoS profile for assignment to one of eight hardware queues in the system that define how the traffic flows with respect to bandwidth, priority, and other parameters. By default, there are two QoS profiles (QP1 and QP8) defined in these supported platforms and PFC works with this default. To segregate the ingress traffic with more granularity, you will want to define other QoS profiles.

  • Priority—The traffic that is paused is based on the priority bits in the VLAN header for tagged packets. You can specify this transmit priority independently from the QoS profile to associate it with the reception of a PFC packets thus giving flexibility in the configuration of the network.

It is suggested that the priority in the VLAN header match the QoS profile priority when traffic ingresses at the edge of the network so that the traffic can be more easily controlled as it traverses through the network.



On Summit X670 and X670V switches, the PFC feature does not support fabric flow control messages on alternate stack ports or SummitStack-V80 native stack ports.

IEEE 802.3x

The following command enables the TX flow-control feature on ports 5 through 7 on a Summit switch:

enable flow-control tx-pause ports 5-7

IEEE 802.1Qbb

The following command enables the priority flow control feature on a Summit switch:

enable flow-control tx-pause priority 3 ports 2


This command was first available in ExtremeXOS 12.1.3.

IEEE 802.1Qbb priority flow control (PFC) was added in ExtremeXOS 12.5.

Platform Availability

IEEE 802.3x

The basic TX-pause and RX-pause functions of this command are available on BlackDiamond X8 switches, BlackDiamond 8000 series modules and Summit family switches.

IEEE 802.1Qbb

The priority function (PFC) is available only on 10G ports and on specific models of the following newer platforms indicated by the part number:
  • BlackDiamond X8 switches.

  • BlackDiamond 8900-10G24X-c modules (manufacturing number 800397-00).

  • BlackDiamond 8900-40G6X-xm modules, 40G ports and 10G ports when in 4x10 partition mode.

  • Summit X460 switches 10G ports.

  • Summit X460-G2

  • Summit X670 switches, 10G ports.

  • Summit X670V switches, 10G and 40G ports.

  • Summit X670-G2

  • Summit X770 40G and 10G ports.