Basically, Multiprotocol BGP EVPN is a control protocol for VXLAN based on industry standards for forwarding within the ACI fabric. Prior to EVPN, VXLAN overlay networks operated in the flood-and-learn mode.

In this mode, both end-host information learning and VTEP (VXLAN tunnel endpoint) discovery are driven over data plane and without using the control protocol to distribute end-host reachability information among VTEPs. VTEP is the end point that is responsible for encapsulating the L2 Ethernet frame in a VXLAN header and forward that on to the transport network.

VXLAN Flood and learn mode

Flood and learn mode is the first and easiest way to deploy Spine-and-Leaf architecture with Cisco Nexus 9000 switches. In this model, switches require flooding to learn about L2 addressing and dependent upon Multicast to discover the BUM (Broadcast Unknowns Multicast). This is how leafs (VTEPs) will learn about adjacent L2 Addresses in the VXLAN Fabric. Plus, STP still takes place in the fabric at L2.

MP-BGP EVPN alters this model. BGP EVPN introduces control-plane learning for end hosts behind remote VTEPs. It provides control-plane and data-plane separation and a unified control plane for both Layer-2 and Layer-3 forwarding in a VXLAN overlay network. Also, this mode minimizes network flooding through protocol-based host MAC/IP route distribution and Address Resolution Protocol (ARP) suppression on the local VTEPs.

BGP EVPN VXLAN Support on Cisco Nexus 9000

After releasing NX-OS Software Release 7.0(3)I1(1), the MP-BGP EVPN control plane for VXLAN is supported for Cisco Nexus 9k and Cisco Nexus 7k. In this release, the Cisco Nexus 9300 platform switches support both the MP-BGP EVPN control-plane functions and the VTEP data-plane functions while the Cisco Nexus 9500 platform switches support the MP-BGP EVPN control-plane functions and VTEP data-plane functions will be added after a maintenance release of Cisco NX-OS 7.0(3)I1(1).

The Cisco Nexus 9300 and 9500 platforms both support inter-VXLAN routing in hardware. The Cisco Nexus 9000 Series is the first switch platform that supports this protocol, the examples are based on the Cisco Nexus 9000 Series

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