Enabling flooding under the BD

[gjstem]

I have read various documents recommending that flooding be enabled to mimic legacy network behavior but i was looking for specific guidance for what scenarios traffic will not reliably work if flooding is disabled under the BD.  My intent was to identify red flag scenarios whereby flooding should be enabled.   As an example, is it correct to assume flooding should be enabled whenever the L3 gateway is external to the fabric?  

[dpita]

Hello 

Thank you for using support forums. First off, what documents are you reading that are requiring having BD Flooding enabled?

As you mentioned, BD Flood is required when the default gateway of endpoints attached to the fabric is located outside the fabric, that is, when the default gateway is not an ACI BD Subnet pervasive, distributed SVI. The only other scenario that comes to mind (it is rather early for me) is L4-L7 integration, but its for the same reason described above...the gateway is outside of the fabric in some cases.

When the gateway is on the fabric then there is no need to flood and actually ACI is optimized for this. ACI will use the distributed gateway instantiated only where there is an endpoint for that default gateway, ACI will also use directed ARPs instead of flooding those. Traffic will work reliably. 

What other questions do you have?

I hope this helps. Have a nice day. 

[gjstem]

Thanks for the clarification.  

Nothing specific from a document perspective, I was just referring to PPT decks that reference enabling flooding for integration with legacy networks as a general recommendation.

I currently have an L2 based network that is connected to an L2 outside EPG for access to a legacy infrastructure but have no requirements for L3 routing.  I have the default BD optimized flooding parameters enabled with no issues thus far.  The L2 network is dedicated for IP storage and the outside EPG connects to a VLAN that spans a series of non-ACI switches providing access to an NFS storage device.  I was looking at ways to showcase securing L2 connectivity to minimize possibilities for services disruption by adding tighter contracts as well as keep unicast + ARP flooding disabled on this connectivity.   I just wanted to be clear on use cases that necessitate flooding to be turned on.

thanks,

Greg