Interconnect 2 ACI Fabric using L3out

[suneq]

Hi experts,

Have anyone interconnected 2 ACI Fabric using L3Out? Are there any difficulties or caveats? 

We have 2 separate Fabric, we want to bring up a dark fiber to interconnect the Border Leafs, establish routing between these 2, we do not need L2 extension and the IP ranges of these 2 Fabric are not overlapped.

We prefer this solution over Multi-site because it's much cheaper and again, we do not need any L2 extension between 2 Fabric, just simple routing. 

Thanks for your advices.

[brunpere]

Hello Suneq,

My name is Bruno Pereira and I’m working in Cisco as a Customer Success Specialist in Data Center and Cloud Networks, so I will try to help you understand the difficulties and caveats of using L3Out to connect two ACI Fabric’s.

I explored this configuration in more depth and there are some key points to take into consideration when you do this type of configuration.

But first, make it very clear that it is entirely possible to interconnect two different sites through L3Out. There are two different types of Layer 3 connectivity that can be established across sites: Intra-VRF Communication and Inter-VRF Communication. So, my advice is to take a look on this website https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-739609.html#CiscoACIMultiSiteperbridgedomainbehavior and explore the content in this chapter “Cisco ACI Multi-Site per bridge domain behavior”.

Some comments about this type of configuration:

1. From a connectivity perspective, to support multi-VRF communication (multi-tenant deployment), the external network interconnecting the fabrics must provide the capability of supporting logically separated routed domains (VRFs or L3VPNs)
2. From a policy perspective, when you have an interconnection of disjoint policy domains, since the policy information is not carried with the data-plane traffic, given that the VXLAN encapsulation is terminated on the border-leaf nodes before sending the traffic to the external routers.
3. Finally, very often the initial requirements of providing Layer-3-only communication across sites evolves into the requirement to stretch IP subnets for various IP mobility use cases. Without Multi-Site, this requires the deployment of a separate Layer 2 Data-Center Interconnect (DCI) technology in the external network, which doesn’t seem relevant to your specific scenario.

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 Cisco ACI 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.