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

Transit routing configuration example

Updated: April 17, 2026

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Describes the components and example values for configuring transit routing between external endpoints through two L3Out connections in a Cisco ACI fabric.

Transit routing is a network configuration that

forwards traffic between external endpoints through multiple L3Out connections,
uses the same tenant and VRF for the L3Out connections, and
uses BGP route reflectors and routing protocols to exchange reachability information between leaf switches.

Configuration components and example values

The transit routing example uses the following components:

A tenant and VRF
A node and interface on leaf switch 101 and leaf switch 102
A primary routing protocol on each L3Out to exchange routes between the border leaf switch and external routers; this example uses BGP
A connectivity routing protocol on each L3Out to provide reachability information for the primary protocol; this example uses OSPF
Two external EPGs
A route map
At least one filter and one contract
An association between the contract and the external EPGs

Table 1. Transit routing example values
Property	L3Out1 on leaf switch 101	L3Out2 on leaf switch 102
Tenant	`t1`	`t1`
VRF	`v1`	`v1`
Node	`nodep1` with router ID `11.11.11.103`	`nodep2` with router ID `22.22.22.203`
OSPF interface	`ifp1` at `eth/1/3`	`ifp2` at `eth/1/3`
BGP peer address	`15.15.15.2/24`	`25.25.25.2/24`
External EPG	`extnw1` at `192.168.1.0/24`	`extnw2` at `192.168.2.0/24`
Route map	`rp1` with `ctx1` and route destination `192.168.1.0/24`	`rp2` with `ctx2` and route destination `192.168.2.0/24`
Filter	`http-filter`	`http-filter`
Contract	`httpCtrct`, provided by `extnw1`	`httpCtrct`, consumed by `extnw2`

Note

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

The following figure shows the transit routing topology for this example.

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