ACI Route Redistribution
- The routes that are learned from the OSPF process on the border leaf are redistributed into BGP for the tenant VRF and they are imported into MP-BGP on the border leaf.
- Import route control is supported for BGP and OSPF, but not for EIGRP.
- Export route control is supported for OSPF, BGP, and EIGRP.
- The routes are learned on the border leaf where the VRF is deployed. The routes are not advertised to the External Layer 3 Outside connection unless it is permitted by the export route control.
 Note | When a subnet for a bridge domain/EPG is set to Advertise Externally, the subnet is programmed as a static route on a border leaf. When the static route is advertised, it is redistributed into the EPG’s Layer 3 outside network routing protocol as an external network, not injected directly into the routing protocol. |
Route Distribution Within the ACI Fabric
ACI supports the following routing mechanisms:
- Static Routes
- OSPFv2 (IPv4)
- OSPFv3 (IPv6)
- iBGP
- eBGP (IPv4 and IPv6)
- EIGRP (IPv4 and IPv6) protocols
ACI supports the VRF-lite implementation when connecting to the external routers. Using sub-interfaces, the border leaf can provide Layer 3 outside connections for the multiple tenants with one physical interface. The VRF-lite implementation requires one protocol session per tenant.
Within the ACI fabric, Multiprotocol BGP (MP-BGP) is implemented between the leaf and the spine switches to propagate the external routes within the ACI fabric. The BGP route reflector technology is deployed in order to support a large number of leaf switches within a single fabric. All of the leaf and spine switches are in one single BGP Autonomous System (AS). Once the border leaf learns the external routes, it can then redistribute the external routes of a given VRF to an MP-BGP address family VPN version 4 or VPN version 6. With address family VPN version 4, MP-BGP maintains a separate BGP routing table for each VRF. Within MP-BGP, the border leaf advertises routes to a spine switch, that is a BGP route reflector. The routes are then propagated to all the leaves where the VRFs (or private network in the APIC GUI’s terminology) are instantiated.
