Which routing protocol is implemented between leaf and spine switches to propagate external routes within the ACI fabric?
The correct answer is B. Multiprotocol Border Gateway Protocol (MP-BGP).
In a Cisco ACI (Application Centric Infrastructure) fabric, the leaf and spine switches use MP-BGP to propagate external routes within the fabric. MP-BGP is a protocol that can support multiple address families, including IPv4 and IPv6, making it well-suited for use in a data center fabric that may need to handle different types of traffic.
When an external route is received by a leaf switch, it is advertised to the spine switches using MP-BGP. The spine switches then propagate the route to other leaf switches in the fabric, ensuring that all devices in the fabric have the necessary routing information to reach external destinations.
MP-BGP is also used to propagate endpoint reachability information within the fabric, allowing the ACI fabric to dynamically adjust its forwarding tables as endpoints move within the fabric.
It is worth noting that while BGP is commonly used for external routing, it is not the only routing protocol that can be used in an ACI fabric. For example, within the fabric itself, Cisco's proprietary Routing and Bridging (R&B) protocol is used for communication between leaf and spine switches. However, for external routing, MP-BGP is the recommended protocol.