Cisco ACI Migration Scenario - Layer 2 trunk

Hello Guys,

I have a question about the migration scenario of a brownfield network towards ACI Greenfield.

I have 2 Data centers seperated physically and i'm going to build a multipod from it.

So the phased approach would be:

• Build the greenfield fabric ACI

• Plan the migration

Now when i build the multipod i will have leafs and spines in each site (2 Spines and 5 leaves each site). This means that when i'm talking about migration. I will have to define a L2out in DC1 and one in DC2 to perform the Layer 2 migration between brownfield and greenfield ACI.

A scenario like this one:

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/migration_guides/migrating_existing_networks_to_aci.html

The brownfield is connected to the ACI with a layer 2 trunk in the form of a double sided vPC. But i will have to foresee 2, because i have 2 data centers. Also the brownfield network has a data center interconnect which is a vPC on it's own.

In order to do the layer 2 migration i have to enable arp flooding and something else on the bridge domain inside ACI because of the traffic leaving ACI again in order to be forwarded/routed to the core switch in the brownfield network (nx-os)

But how will that work with 2 data centers? Say i have the vlan moved into the ACI fabric with the way out still being that L2out EPG in a single DC, what if that vlan has also been trunked across the brownfield data center DCI and ends up in the other DC. Won't i make my core switches go haywire for seeing mac address across the vPC doing the DCI and across the vPC going towards the ACI?

Or will this only happen in a scenario i have an active host in both data centers on that same vlan? Then i could manipulate the way ACI sends the traffic out by adding the L2out to the Bridge domain?