L3OUT Export Prefixes

[snarayanaraju]

Hello All - Want to know how to Export a Route learned from one L3OUT to another L3OUT.

The Scenario:

L3OUT-A with eBGP configured. External Router is advertising subnet 192.168.1.0/24 into ACI

L3OUT-B with eBGP configured.  External Router is advertising subnet 172.16.1.0/24 into ACI

All these L3OUTs is in the same Tenant and VRF

Requirement:

192.168.1.0/24 has to be advertised out L3OUT-B

172.16.1.0/24 has to be advertised out L3OUT-A

External Routed Network -> L3OUT-TO-ASIDE -> Networks -> EPG-ROUTER_A

     defined network 172.16.1.0/24 and Marked it as EXPORT ROUTE CONTROL SUBNET    

External Routed Network -> L3OUT-TO-BSIDE -> Networks -> EPG-ROUTER_B

     defined network 192.168.1.0/24 and Marked it as EXPORT ROUTE CONTROL SUBNET    

Question: What to be configured under Route Maps/Profile for these routes to get exported from corresponding L3OUTs? 

I read, By default, Cisco ACI will not advertise routes learned from one L3Out back out another L3Out.Transit routing is controlled by creating export route control policies for the L3Out. Export route control policies control which transit prefixes are redistributed into the L3Out protocol. These policies will be instantiated on the leaf switch as route maps and IP prefix-lists.

Thanks, Sairam

[kumar.rb@cognizant.com]

Adding another question: What is the purpose of the ROUTE-MAP/PROFILE when we can specify the exact Subnet & Prefixes Under Network and mark it as "EXPORT ROUTE CONTROL SUBNET"?

Practically I am seeing a case, where we configured a subnet 10.100.0.0/16 in Network and marked it as EXPORT ROUTE CONTROL.  And under ROUTE-MAP/PROFILE we have various other subnets like 10.161.0.0/24 for example. 

I see both 10.100.0.0/16 and 10.161.0.0/24 is getting advertised out of the L3-OUT. 

What are the fundamentals behind the ROUTE-MAP/PROFILE and EXPORT ROUTE CONTROL SUBNET

[snarayanaraju]

Hello Experts - Any chance the questions can be answered to get some clarity