Cisco APIC Layer 3 Networking Configuration Guide, Release 6.2(x)

Transit routing in the ACI fabric

Updated: April 17, 2026

Want to summarize with AI?

Describes how the Cisco ACI fabric acts as a transit MP-BGP domain to exchange routes between external Layer 3 domains through L3Out connections.

Transit routing in the Cisco ACI fabric is a network configuration that

advertises routes from one L3Out to another L3Out in the same tenant and VRF,
supports multiple L3Out connections on border leaf switches, and
uses the fabric as a transit MP-BGP domain between external peers.

Route advertisement and distribution

Cisco APIC supports external Layer 3 connectivity through OSPF NSSA and iBGP. The fabric advertises tenant bridge domain subnets to external routers through L3Out connections.

For each VRF, the ingress leaf imports routes that it learns from external routers into MP-BGP. The fabric exports those routes only to leaf switches on which the tenant VRF is deployed.

Note

For cautions and guidelines for configuring transit routing, see Transit routing guidelines .

Need help?

Open a support case

(Requires a Cisco Service Contract)

The documentation set for this product strives to use bias-free language. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. Learn more about how Cisco is using Inclusive Language.