Hi,
Please verify the five important functions of L3out:
1. Learn external routes via routing protocols (or static routes)
2. Distribute learned external routes (or static routes) to other leaf switches
3. Advertise ACI internal routes (BD subnets) to outside ACI
4. Advertise learned external routes to other L3Outs (Transit Routing)
5. Allow traffic to arrive from or be sent to external networks via L3Out by using a contract
And to know more about L3out BGP configuration, do check this link:
https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/guide-c07-743150.html#L3OutBGP
If the issue still persists after checking from this link, please raise a TAC case to do live troubleshooting.
If you find my reply solved your question or issue, kindly click the 'Accept as Solution' button and vote it as helpful.
You can also learn more about Cisco ACI through our live Ask the Experts (ATXs) session. Check out the ATXs Resources [https://community.cisco.com/t5/data-center-and-cloud-knowledge/cisco-aci-ask-the-experts-resources/ta-p/4394491] to view the latest schedule for upcoming sessions, as well as the useful references, e.g. online guides, FAQs.
Thanks and regards,
Tarakesh Jetti
Customer Success Specialist - CX Team.