c869d905ba
Handling of unknown MACs on an bridge with incomplete learning capabilites (aka uplink ports) can be defined in different ways. The classical approach is to broadcast unicast frames send to an unknown MAC, because the unknown devices can be everywhere. This mode is default for ng_bridge(4). In the case of dedicated uplink ports, which prohibit learning of MAC addresses in order to save memory and CPU cycles, the broadcast approach is dangerous. All traffic to the uplink port is broadcasted to every downlink port, too. In this case, it's better to restrict the distribution of frames to unknown MAC to the uplink ports only. In order to keep the chance small and the handling as natural as possible, the first attached link is used to determine the behaviour of the bridge: If it is an "uplink" port, then the bridge switch from classical mode to restricted mode. Reviewed By: kp Approved by: kp (mentor) MFC after: 2 weeks Differential Revision: https://reviews.freebsd.org/D28487
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