Traffic distribution Intelligent over COMMON_L3_Out

[NDP]

Could someone please clarify on the following

(i) L3Out in COMMON Tenant

(ii) two VRFs in Tenant UAT ( VRF A, BD A_UAT--> 10.0.0.0/24 VRF B,BD B_UAT -->10.0.1.0/24)

(iii) two VRFs in Tenant PROD ( VRF C BD C_PROD-->10.0.3.0/24, VRF D BD D_PROD-->10.0.4.0/24)

All four bridge domains are associated with the L3Out created in COMMON Tenant. when external network tried to talk to anyone of the networks specified above, they would send traffic to next hop IP of ACI which is Fabric IP of COMMONL3Out. 

how does ACI fabric now forward the traffic to proper VRF ( if destination in the received packet is 10.0.0.0/24, how does it know that packet should go to VRF A ).

Thank you in advance

[Rick1776]

It know's it via the VNID.

See the below Link.
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/1-x/ACI_Best_Practices/b_ACI_Best_Practices/b_ACI_Best_Practices_chapter_010010.html#d13726e1306a1635

[gmonroy · Accepted solution]

NDP,

    Assuming your COMMON_L3_OUT is within its own VRF, you would have to use some route leaking configuration within ACI to get across VRFs.

Essentially what will end up happening is that each respective VRF can have the routes learned from your L3out that may point to the overlay as it's next hop (to get from VRF A to VRF COMMON's L3out, for instance).

In VRF COMMON, you will have routes from each of your BD Subnets pointing into the Overlay so that they could eventually get back to their VRF where the subnet is originating. 

Here is a (slightly older) document that outlines one method of route leaking and some verification output:

https://www.cisco.com/c/en/us/support/docs/cloud-systems-management/application-policy-infrastructure-controller-apic/200242-Configuring-Inter-Context-Communication.html

-Gabriel

[Rick1776]

I really like this picture as well to explain.