Understanding the vLAG Forwarding Rule
In order to prevent potential duplication of multicast or broadcast traffic, a forwarding rule is installed on all ports that are part of vLAGs to drop traffic whose ingress point is the cluster links. This rule is shown in the figure below:
Figure 7-12 - vLAG Forwarding Rule
The figure above shows a packet entering cluster switch PN-0 that needs to be sent out to Host 1 over the vLAG. To prevent duplication of traffic on the vLAG, any traffic traversing the cluster links and egressing on vLAG ports on cluster switch PN-1 is dropped.