Describes how routing mechanisms and protocols distribute routes within and outside the ACI fabric infrastructure.
Route distribution within the ACI fabric is a networking mechanism that
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supports multiple routing protocols including static routes, OSPFv2, OSPFv3, iBGP, eBGP, and EIGRP protocols
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implements Multiprotocol BGP (MP-BGP) between leaf and spine switches to propagate external routes within the ACI fabric
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uses BGP route reflector technology to support a large number of leaf switches within a single fabric, and
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supports VRF-lite implementation for connecting to external routers with multiple tenants using one physical interface.
Supported routing mechanisms
ACI supports these routing mechanisms:
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Static Routes
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OSPFv2 (IPv4)
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OSPFv3 (IPv6)
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iBGP
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eBGP (IPv4 and IPv6)
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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.