Programming interface MAC filter without enabling PROMISC on an interface from user space.

[Tom Judge]

Bruce M. Simpson wrote:
> Tom Judge wrote:
<SNIP>
>> Personally I can't see why this approach would be a problem,  but I am 
>> not a expert.  The address is defined in IEEE Std 802.1D-2004 as to 
>> not be forwarded by bridges (which I interpret as it being link local 
>> in a sense as switches/bridges are not allowed to forward the frame), 
>> so I can't see it being a problem registered on multiple interfaces.
> 
> SIOCADDMULTI memberships are specific to the interface you request them 
> on. I can't speak for the bridging code -- I don't think it does any 
> special handling of multicast frames, however I'm not sure if it's smart 
> enough not to forward this group. Like IN_LOCALGROUP() it might need its 
> own 'don't forward this' clause.
> 


Just for the record it seems that if_bridge replaces the destination MAC 
of a Ethernet multicast packet with its own MAC therefore making sure 
that the packets are not forwarded.  Andrew can you confirm this 
assumption?  (Based on sys/net/if_bridge.c lines 2011-2018 on RELENG_6_2)

Tom