For folks who are looking to enable ACI transit routing functionality, there a couple of CCO sites that are must reads. Don’t sign off on your L3out design with transit routing until you have read the documents below!
The ACI Best Practices Guide focuses on supported topologies, guidelines and limitations, and even recommended configurations for transit routing. It has very detailed design recommendations and caveats for each of the routing protocols.
The Cisco APIC and Transit Routing document has a supported combination matrix detailing transit routing protocol combinations, and which are supported. It serves as a quick reference guide for those who need to validate that what they are designing is in fact, supported.
|Route control Setting||Use||Options|
|Export Route Control||To allow the prefixes that are advertised to the external peers. Implemented with IP prefix-lists.||Specific match (prefix and prefix length).|
|Import Route Control||To allow prefixes that are inbound from the external BGP and OSPF peers. Implemented with IP prefix-lists.||Specific match (prefix and prefix length) .|
|Security Import Subnet||To permit the packets between two prefix based EPGs. Implemented with ACLs.||Uses the ACL match prefix/wildcard match rules.|
|Aggregate Export||To allow all prefixes to be advertised to the external peers. Implemented with 0.0.0.0/ le 32 IP prefix-list.||Only supported for 0.0.0.0/0 subnet (all prefixes).|
|Aggregate Import||To allow all prefixes that are inbound from an external BGP peer. Implemented with 0.0.0.0/0 le 32 IP prefix-list.||Only supported for 0.0.0.0/0 subnet (all prefixes).|