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Control Link Local Multicast

Cumulus Linux provides a configuration option on Broadcom switches to disable forwarding of link-local multicast packets to the CPU so that such packets only flood the ASIC, which reduces CPU usage.

Switches with the Trident3 ASIC do not support this option.

To disable forwarding of link local multicast packets to the CPU on a Broadcom switch, run the following command:

cumulus@switch:~$ echo TRUE > /cumulus/switchd/config/hal/bcm/ll_mcast_punt_disable

The configuration above takes effect immediately, but does not persist if you reboot the switch.

To apply the configuration so that it is persistent, edit the /etc/cumulus/switchd.conf file and uncomment the hal.bcm.ll_mcast_punt_disable = TRUE option. For example:

cumulus@switch:~$ sudo nano /etc/cumulus/switchd.conf
# /etc/cumulus/switchd.conf - switchd configuration file
# Bridge L2MC Link-Local multicast punt disable
hal.bcm.ll_mcast_punt_disable = TRUE

A switchd restart is not required.