ACI Export Control Subnet

[snarayanaraju]

Hello All - Please help me giving clarity on this topic " EXPORT ROUTE CONTROL" in ACI.

After studying a lot of articles on this, still, I am not able to conclude the behavior of "EXPORT ROUTE CONTROL"

Scenario:

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

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

Bridge domain BD-C is configured with L3 subnet IP 10.1.1.0/24 

Bridge domain BD-D is configured with L3 subnet IP 10.1.2.0/24

Question:

1) What role ROUTE CONTROL EXPORT option plays here in adverting BD subnets out of L3OUTs?

2) My understanding is Transit Routing between L3OUT-A and L3OUT-B is not possible unless ROUTE CONTROL SUBNET is enabled.

3) If the ROUTE CONTROL SUBNET is enabled, should the Route Policy (Eg:Default Export) has to be applied? Without applying Route Export Policy along with ROUTE CONTROL POLICY , will the Routes are advertised out L3OUTs?

Thanks in advance, Sairam

[6askorobogatov]

1) What role ROUTE CONTROL EXPORT option plays here in adverting BD subnets out of L3OUTs?

Not the BD subnet, subnet define in L3Out External EPG and existed in VRF route table (it could be route leak from another VRF) With "Export Route Control Subnet"  route map for export will be used to match prefix, prepend etc. 

2) My understanding is Transit Routing between L3OUT-A and L3OUT-B is not possible unless ROUTE CONTROL SUBNET is enabled.

Not exactly. . You need to "Shared Route Control Subnet" (leak route) and "Shared Security Import Subnet" (permit traffic in another VRF)

3) If the ROUTE CONTROL SUBNET is enabled, should the Route Policy (Eg:Default Export) has to be applied?

yes

Without applying Route Export Policy along with ROUTE CONTROL POLICY , will the Routes are advertised out L3OUTs?

Yes with "External Subnets for the External EPG"

[snarayanaraju]

Thanks for your the response

This below link is also useful for reading in this matter

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/4-x/L3-configuration/Cisco-APIC-Layer-3-Networking-Configuration-Guide-401/Cisco-APIC-Layer-3-Networking-Configuration-Guide-401_chapter_011000.html