VXLAN and BGP EVPN
VXLAN stands for Virtual eXtensible Local Area Network. It is a network virtualization technology that creates a Layer 2 (Ethernet) overlay network on top of an existing Layer 3 (IP) physical network infrastructure. VXLAN was designed to solve the scalability and flexibility problems of traditional VLANs, particularly in large data centers and cloud computing environments that need to support thousands of tenants and enable workload mobility.
BGP EVPN is a critical evolution in data center networking because it replaces older, inefficient methods of network learning (known as "flood and learn") with a scalable, intelligent control plane mechanism using BGP extensions.
How BGP EVPN Works
BGP EVPN uses the widely adopted Border Gateway Protocol (BGP)—specifically, an extension called Multiprotocol BGP (MP-BGP)—to exchange information about network endpoints (servers, VMs, etc.) across the network fabric. In a typical deployment using VXLAN (Virtual eXtensible LAN) overlays, the process works as follows:
- VXLAN (Data Plane): Handles the encapsulation and tunneling of data packets over a physical Layer 3 IP network (the underlay).
- BGP EVPN (Control Plane): Manages the learning and advertisement of network reachability information between the devices that create the tunnels (VTEPs - VXLAN Tunnel Endpoints).
- MAC/IP Learning: When a server connects to a switch (leaf switch/VTEP), the local VTEP learns the server's MAC address and IP address locally.
- BGP Advertisement: Instead of relying on flooding the network to find a destination (like older VLAN systems or basic VXLAN implementations did), the VTEP immediately advertises the host's MAC and IP address information to all other VTEPs via MP-BGP routes.
- Automatic Discovery & Tunneling: Receiving VTEPs read this advertisement and update their local forwarding tables. This allows VTEPs to dynamically discover each other and establish VXLAN tunnels on demand, without manual configuration.
