How does Pinning work.
If you look at the image below pinning can be either dynamic or static via a pinning group that is configured in UCS Manager under the LAN tab.
In this example vNIC 1 (blue) is dynamically pinned to the port-channel between IOM A to FI-A that goes up to N5K1. vNIC2 (Green) is statically pinning to a single port form FI-A to N5K2. So if N5K1 has to talk to MAC 00B1 it would have to transverse to N5K2 down the particular port down to FI-A.
Remember that all FI's in End Host Mode (EHM) act as end host to the upstream switches so no MAC learning takes place North of the FI's
Each FI's picks a port (could be a Port-Channel) to be the Multicast or Broadcast Receiver port. This is not configurable. In the above example the orange ports are the Broadcast/MultiCast receiver port, if a Broadcast/MultiCast is received on a port other then the assigned Broadcast/MultiCast port it will be dropped.
You can see what he Multicast/BroadCast receiver port with the command
show platform software enm internal info vlandb all
Deja Vu Check
Also in the above example if FI-A (sourced from vNIC2 (greeN)sends out the Broadcast/MultiCast packet and it is received on the same (blue) port-channle, through the DeJa Vu check it will drop the packet because it's seen it before that was sent by vNIC2 (green).
RPF (Reverse path forwarding Check)
If traffic form MAC 00A1 is trying to come in via N5K2 to FI-A it will the fail the RPF check and the traffic will be dropped. MAC 00A1 is only allowed on N5K1 (blue) port-channel.
If you have a static pinning on vNIC1 (blue) that is configured for the port-channel from FI-A if that port-channel fails but all other ports in FI-A are operational it will not fail over to another port on FI-A, if you configured Failover in the static pinning it will failover to FI-B.