Explains how to configure transit routing in a ACI fabric. It covers enabling traffic flow between endpoints through multiple L3Outs connected to external routers using BGP and OSPF. Key configurations include tenant and VRF, leaf switch interfaces, external EPGs, route maps, filters, and contracts. The fabric acts as a transit MP-BGP domain, advertising routes between L3Outs for full IP connectivity while behaving as a stub network internally
This chapter contains the following sections:
Transit routing in the ACI fabric
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 Use Cases
Describes how transit routing enables connectivity between multiple Layer 3 domains, mainframes, service nodes, multipod topologies, and GOLF configurations in ACI fabric environments. Provides context for integrating external and internal network resources.
Supported transit-routing combinations
Lists supported, unsupported, and tested transit-routing combinations for L3Out connections that use OSPF, iBGP, eBGP, EIGRP, or static routes between external routing domains.
Transit routing guidelines
Describes route-tag, route-control, hardware, MTU, and subnet-advertisement requirements for configuring stable transit routing connections across external networks in a Cisco ACI fabric.
Transit route control
Describes how L3Out policies control route import and export, default-route leaking, route attributes, and BGP or OSPF configuration for transit routing.
Subnet scope and aggregate controls
Describes subnet scope and aggregate controls that manage route advertisement, route sharing, security-policy enforcement, and prefix aggregation for external EPGs and L3Outs.
Transit routing configuration example
Describes the components and example values for configuring transit routing between external endpoints through two L3Out connections in a Cisco ACI fabric.
Configure Transit Routing Using the GUI
Configures transit routing for a tenant using the GUI by deploying two L3Outs in one VRF on two border leaf switches connected to separate routers. Provides step-by-step instructions for creating tenants, VRFs, L3Outs, contracts, filters, and associating EPGs for transit routing.
Lists supported, unsupported, and tested transit-routing combinations for L3Out connections that use OSPF, iBGP, eBGP, EIGRP, or static routes between external routing domains.