In RouterOS v6.41rc1+ and later OS versions (and also in 6.40 rc36-rc40), there is a new bridge implementation that supports hardware offloading (hw-offload).

This update will convert all interface "master-port" configuration into new bridge configuration, and eliminate the switch  "master-port" option.

The bridge will handle all layer 2 (L2) forwarding and the use of switch-chip (hw-offload) will be automatically turned on based on appropriate conditions.

The rest of RouterOS Switch specific configuration remains untouched in usual menus for now.

More info on the rc41 forum.

RouterOS 6.41 contains new bridge implementation that supports hardware offloading (hw-offload).
This update will convert all interface "master-port" configuration into new bridge configuration, and eliminate "master-port" option as such.
Bridge will handle all Layer2 forwarding and the use of switch-chip (hw-offload) will be automatically turned on based on appropriate conditions.
The rest of RouterOS Switch specific configuration remains untouched in usual menus for now.
Please, note that downgrading to previous RouterOS versions will not restore "master-port" configuration, so use backups to restore configuration on downgrade.
Final release of new 6.41 bridge implementation.