Forwarding broadcast, multicast, and unknown traffic

In the example shown in Broadcast/multicast/unknown traffic flow access DT switches, multicast/broadcast/unknown traffic from Host X or Y is always forwarded by Switch A over one of its standard 802.3ad trunk links to either Switch B or C. Switch B or C forwards the traffic on all the links including the ISC port, but not on the port that the traffic was received on. The peer DT switch (B or C) that receives broadcast/multicast/unknown traffic over the ISC port does not forward the packets to any of the DT trunks; the packet is sent only over the non-DT ports. The one exception is if the DT trunk on the peer aggregation device is down, then traffic received over the ISC is forwarded to the corresponding DT trunk.