Question

When extending Layer 2 domains across a routed Layer 3 fabric using VXLAN, what control plane protocol is used to distribute MAC address reachability information?

Accepted Answer

The control plane protocol used to distribute MAC address reachability information in a VXLAN fabric is Multiprotocol Border Gateway Protocol, commonly referred to as MP-BGP or BGP EVPN. In a standard VXLAN environment, MAC addresses are traditionally learned through data plane flooding, where every switch broadcasts traffic to find a destination, which is inefficient and scales poorly. MP-BGP solves this by acting as a centralized control plane. When a Virtual Tunnel Endpoint, which is the network hardware that encapsulates and decapsulates VXLAN packets, learns a new MAC address on a local port, it uses MP-BGP to advertise this information to all other switches in the fabric. This advertisement includes the MAC address, the associated Layer 2 segment identifier, and the IP address of the originating switch. By using MP-BGP, switches build a table of remote MAC addresses and their corresponding tunnel endpoints without needing to flood traffic across the network. This process is specifically defined by the Ethernet VPN, or EVPN, address family within BGP, which allows for the efficient exchange of Layer 2 and Layer 3 reachability information across a Layer 3 routed core.

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When extending Layer 2 domains across a routed Layer 3 fabric using VXLAN, what control plane protocol is used to distribute MAC address reachability information?

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