Configure IEEE 802.3X Pause Frame Transmit

About this task

Configure IEEE 802.3X Pause frame transmit to eliminate or minimize packet loss.

By default, flow control mode is disabled. When disabled, the system does not generate nor configure the transmission of flow control messages. The system always honors received flow control messages regardless of the flow control mode status. You must enable this mode before you configure an interface to send pause frames.

By default, an interface does not send pause frames.

Note

If you enable MACsec on an interface and you send small packet size traffic near line rate, the In FlowCtrl frame might increment in the output of the show interfaces gigabitEthernet statistics command because of the processing overhead caused by adding the MACsec header of 32 bytes. This is part of the expected over-subscription footprint.

1. Enter Global Configuration mode:

   enable

   configure terminal

2. Enable flow control mode:

   boot config flags flow-control-mode

3. Save the configuration.
4. Return to Privileged EXEC mode:

   end

5. Reboot the chassis.

   boot

6. Enter GigabitEthernet Interface Configuration mode:

   enable

   configure terminal

   interface GigabitEthernet {slot/port[/sub-port][-slot/port[/sub-port]][,...][slot/all][all]}

   

   Note

   If the platform supports channelization and the port is channelized, you must also specify the sub-port in the format slot/port/sub-port.

7. Configure the interface to generate pause frames:

   tx-flow-control [enable]

8. Optional: Configure other interfaces to generate pause frames:

   tx-flow-control port {slot/port[/sub-port][-slot/port[/sub-port]][,...][slot/all][all]} enable

9. Verify the boot flag configuration:

   show boot config flags

10. Verify the interface configuration:

    show interfaces gigabitEthernet l1-config {slot/port[/sub-port][-slot/port[/sub-port]][,...][slot/all][all]}

11. View the pause-frame packet count:

    show interfaces gigabitEthernet statistics {slot/port[/sub-port][-slot/port[/sub-port]][,...][slot/all][all]}

Example

Enable flow control on the system and configure slot 1, port 10 to send pause frames. Verify the configuration.

Switch:1>enable
Switch:1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Switch:1(config)#boot config flags flow-control-mode
Warning: Please save the configuration and reboot the switch
         for this configuration to take effect.
Switch:1<config>#save config
CP-1: Save config to file /intflash/config.cfg successful.
CP-1: Save license to file /intflash/license.xml successful.
Switch:1<config>#disable
Switch:1#boot
Are you sure you want to re-boot the switch (y/n) ?y

Note

Flag support can vary across hardware models.

Switch:1#show boot config flags
flags advanced-feature-bandwidth-reservation low
flags block-snmp false
flags debug-config false
flags debugmode false
flags dvr-leaf-mode false
flags enhancedsecure-mode false
flags factorydefaults false
flags flow-control-mode true
flags ftpd true
flags hsecure false
flags ipv6-egress-filter true
flags ipv6-mode false
flags linerate-directed-broadcast false
flags logging true
flags nni-mstp false
flags reboot true
flags spanning-tree-mode mstp
flags spbm-config-mode true
flags sshd true
flags syslog-rfc5424-format true
flags telnetd true
flags tftpd true
flags trace-logging false
flags urpf-mode true
flags verify-config true
flags vrf-scaling true
flags vxlan-gw-full-interworking-mode false

Switch:1(config-if)#show interfaces gigabitEthernet l1-config 1/10
==================================================================================================
                                          Port Config L1
==================================================================================================
PORT     AUTO  OPERATE  CUSTOM AUTO NEGOTIATION CANA    ADMIN     OPERATE   ADMIN        OPERATE
NUM      NEG.  AUTO-NEG ADVERTISEMENTS          ORIGIN  DPLX SPD  DPLX SPD  TX-FLW-CTRL  TX-FLW-CTRL
--------------------------------------------------------------------------------------------------
1/10     true  true     Not Configured          RADIUS   full 10000  0           enable       enable

View the pause-frame packet count for slot 1, port 10.

Switch:1(config-if)#show interfaces gigabitEthernet statistics 1/10
==========================================================================================
                                          Port Stats Interface
==========================================================================================
PORT     IN             OUT                  IN                   OUT                  
NUM    OCTETS          OCTETS               PACKET               PACKET               
------------------------------------------------------------------------------------------
1/1    29964704384     22788614528          234106526            178034166            
	
PORT     IN             OUT                 IN                   OUT            OUTLOSS    
NUM    FLOWCTRL        FLOWCTRL             PFC                  PFC            PACKETS    
------------------------------------------------------------------------------------------
1/1    0               11014                0                    0             0