We are planning to migrate the Gateway of all the vlans to ACI. Currently the Gateway is a pair of Nexus 7K and this pair has a Layer 2 Extension to ACI, as well a Layer 3 Out. 90% of the servers are outside ACI, on the Traditional Network, but still customer want to migrate gateway to ACI to prepare for App Centric.
My question is, regarding to have most of the server/services outside ACI, the BD configuration for all these vlans should be in flood, flood, flood, flood in BD, or should I use Hardware proxy and optimized flood, because now is going to be the gateway?
We have some servers in ACI and are using the layer 2 extension to reach their gateways on the Nexus 7K, those EPGs and BD are configured as flood, but now that the gateway is going to be ACI, Im not sure if they will continue having the same configuration, or if it is changed till most of servers are in ACI.
Flood is typically needed when a resource is external to ACI such as a GW located on the N7K and endpoints need to be able to resovle ARP for it. In your case since you have migrated the GW to ACI, and you have a simple L2 extension to the endpoints, you don't really need to keep the BDs in Flood mode assuming the endpoints are relatively chatty (non-silent). My typically advice would be to just leave the BD in flood mode until the majority if not all endpoints have been migrated to ACI. At that point you can change the BD mode from Flood to Proxy. At this point is typically when the connection between ACI and your legacy environment becomes L3 only. There's no real harm keeping the BD in flood mode. Just means ACI will operate those BDs in more of a legacy behavior (same as how your N7K handles unknown unicast) for the time being. It will not make any operational impact otherwise. Proxy mode is just an optimization to traffic handling.