I have a question: Let say I have a VN where most devices are silent hosts. I have a controller which is connected to one of the Edge gateways and when I enable Layer 2 Flooding for this VN, Multicast traffic sent from this controller is flooded to these silent hosts from other Edge devices. Now question: Let`s say I want this Controller to sit outside of Fabric in VM server which is connected to Core and Core in its turn connected to Border. NOW, Will flooding work from controller, if I configure L2 Handoff for this VN between Border and Core and then extend this L2 to VM. I mean will traffic flooded to edge and then to silent hosts?
The feature you are looking for is something called IP directed broadcast in DNAC 2.1.2.x
A controller outside the fabric sends a magic packet, which is an SDB (subnet directed broadcast, a broadcast packet for a subnet from a source not on that subnet), this packet is received on a special SVI created by DNAC to forward that broadcast inside the fabric.
Only Cat9k fabrics are supported, starting from 17.3.1 and onwards. L2 flooding is enabled (with flood unknown-unicast under L2 instance) once this feature is enabled.