Configuring link level flow control

Link level flow control (LLFC) allows a congested receiver to communicate a PAUSE frame to a transmitter to stop data transmission until the congestion is cleared.

Before you begin

Before configuring LLFC on an interface or a port channel, Extreme recommends that you stop the traffic on the interface.

About this task

LLFC can be configured only at the interface level.

Perform the following steps to configure LLFC.

Procedure

Enter global configuration mode.
```
device# configure terminal
```

Enter interface configuration mode.

device(config)# interface ethernet 3/18

Enable LLFC in the transmission and reception directions for the port.
```
device(conf-eth-3/18)# qos flowcontrol tx on rx on
```
Return to privileged EXEC mode.
```
device(conf-eth-3/18)# end
```

Verify the configuration.

device# show qos flowcontrol interface ethernet 3/18
Interface Ethernet 3/18
  Mode 802.3x
     TX    RX         TX Output Paused    RX
  Admin Admin     Frames  512 BitTimes    Frames
  -----------------------------------------------
     On    On

Save the configuration.

device# copy running-config startup-config

LLFC configuration example

device# configure terminal
device(config)# interface ethernet 3/18
device(conf-eth-3/18)# qos flowcontrol tx on rx on
device(conf-eth-3/18)# end
device# show qos flowcontrol interface ethernet 3/18
device# copy running-config startup-config

Displaying flow control information and clearing its statistics

You can display flow control information for all interfaces, a specific Ethernet interface, or a port channel. This information includes the flow control mode, generation (Tx) and reception (Rx) status, and Tx and Rx PAUSE frame counts.

The following example shows how to display the flow control information for all interfaces.

device# show qos flowcontrol interface all 
Interface Ethernet 0/1
  Mode Off
Interface Ethernet 0/2
  Mode Off
Interface Ethernet 0/3
  Mode Off
Interface Ethernet 0/4
  Mode Off
...
  Mode 802.3x
     TX    RX         TX Output Paused    RX
  Admin Admin     Frames  512 BitTimes     Frames
  -----------------------------------------------
     Off   On          0                        0

The following example displays the flow control information on a specific interface.

device# show qos flowcontrol interface ethernet 0/18
Interface Ethernet 0/18
  Mode 802.3x
     TX    RX         TX Output Paused    RX
  Admin Admin     Frames  512 BitTimes     Frames
  -----------------------------------------------
     Off   On          0                        0

You can also clear the flow control statistics for all interfaces, a specific Ethernet interface, or a port channel. The following example clears the statistics for all interfaces.

device# clear qos flowcontrol interface all

The following example clears the flow control statistics on a specific interface.

device# clear qos flowcontrol interface ethernet 0/18