Configuring Egress Multicast Buffering

Egress Multicast Buffer

Effective with Cisco NX-OS Release 7.2(0)N1(1), the Cisco Nexus 5600 and 6000 series switches support egress multicast buffer tuning.

Information About Egress Multicast Buffering

The egress multicast buffer allows additional cells to enhance multicast traffic at egress. When there is heavy multicast traffic, buffer space (cells) is borrowed from the unicast pool. The pool provides a specific number of cells to enhance the burst absorption and minimize traffic drops at egress.


Note

The egress multicast buffering feature is enabled only in multicast heavy traffic environment. Also, there is a set limit for the multicast pool size (the number of cells that can be borrowed).

You can configure multicast traffic buffering when the traffic patten in your environment has:

  • Multicast traffic counts 90 to 99 percent

  • Multicast traffic is inconsistent

Configuring Egress Multicast Buffer Tuning

Procedure
     Command or ActionPurpose
    Step 1switch# configure terminal  

    Enters global configuration mode.

     
    Step 2switch(config)# hardware multicast-buffer-tune  

    Tunes the egress multicast buffer size to have more burst absorption.

     

    The following example shows how the egress multicast buffer size is tuned to have more burst absorption. 

    switch# configure terminal
switch(config)# hardware multicast-buffer-tune

    Verifying Egress Multicast Buffering

    To verify the egress multicast buffering, use the following command:

    Command

    Purpose

    switch# show platform software qd info

    Displays the status of the multicast buffer enable feature, the allocated space for egress buffer, and number of cells in unicast and multicast pool in 40G and 10G fabric modes.

    The following example shows how to verify cells values in unicast and multicast pool before enabling the egress multicast buffer command. 

    Switch# show platform software qd info

Multicast buffer enable feature is : Disabled //verifying unicast 
and multicast cell values when multicast 
buffer feature is disabled//

Egress buffer allocation
Fabric mode : 40G Fabric Mode
      10G Port                        40G Port
pool| total| xoff|  xon| xcos| cls|   total| xoff|  xon| xcos| cls 
uc 0|   100|   60|   30|    0|  00|     100|   60|   30|    0|  00  
uc 1|     0|    0|    0|    0|  00|       0|    0|    0|    0|  00  
uc 2|     0|    0|    0|    0|  00|       0|    0|    0|    0|  00  
uc 3|  1035|  700|   16|  350|  fe|    1934| 1512|   64| 1112|  fe  
mc 0| 13292|    0|    0|  -  |  ff|   20666|    0|    0|  -  |  ff  
mc 1|     0|    0|    0|  -  |  00|       0|    0|    0|  -  |  00

    The following example shows how to verify cell values in unicast and multicast pool after enabling the egress multicast buffer command: 

    Switch# show platform software qd info

Multicast buffer enable feature is : Enabled //verifying unicast and 
multicast cell values when multicast 
buffer feature is enabled//

Egress buffer allocation
Fabric mode : 40G Fabric Mode
      10G Port                        40G Port
pool| total| xoff|  xon| xcos| cls|   total| xoff|  xon| xcos| cls
uc 0|   100|   60|   30|    0|  00|     100|   60|   30|    0|  00
uc 1|     0|    0|    0|    0|  00|       0|    0|    0|    0|  00
uc 2|     0|    0|    0|    0|  00|       0|    0|    0|    0|  00
uc 3|   451|  116|   16|   87|  fe|     586|  164|   64|  123|  fe
mc 0| 20300|    0|    0|  -  |  ff|   24710|    0|    0|  -  |  ff
mc 1|     0|    0|    0|  -  |  00|       0|    0|    0|  -  |  00