Hi there everyone,
Today I will tell you about EVPN and its basic concepts.
Basic Concepts of EVPN
Why is EVPN developed? In the initial VXLAN solution (RFC 7348), no control plane is defined. VXLAN tunnels are manually configured, and host addresses are learned through traffic flooding. This method is easy to implement, but it causes a lot of flooding traffic on the network and makes network expansion difficult.
To solve the preceding problems, EVPN is introduced as the control plane of VXLAN that is a network virtualization overlay (NVO) protocol, as shown in Figure 1-1. EVPN can also function as the control plane of some other protocols. This document describes only information about EVPN functioning as the control plane of VXLAN.
Figure 1-1 EVPN functioning as the control plane of VXLAN
EVPN uses the MP-BGP mechanism. Before understanding fundamentals of EVPN, let's review MP-BGP.
Traditional BGP-4 peers use Update messages to exchange routing information. An Update message can advertise reachable routes with the same path attribute. These routes are carried in the Network Layer Reachability Information (NLRI) field. BGP-4 can manage only IPv4 unicast routing information, so MP-BGP was developed to support multiple network layer protocols, such as IPv6 and multicast. MP-BGP extends NLRI based on BGP-4. After extension, the description of the address family is added to NLRI to differentiate network layer protocols, such as the IPv6 unicast address family and VPN instance address family.
Similarly, EVPN uses the MP-BGP mechanism and defines a new sub-address family, EVPN address family, in the L2VPN address family. In the EVPN address family, a new type of NLRI is added, that is, EVPN NLRI. EVPN NLRI defines several types of BGP EVPN routes, which can carry information such as the host IP address, MAC address, VNI, and VRF. After a VTEP learns the IP address and MAC address of a connected host, the VTEP can send the information to other VTEPs through MP-BGP routes. In this way, learning of host IP address and MAC address information can be implemented on the control plane, suppressing traffic flooding on the data plane.
Using EVPN as the control plane of VXLAN has the following advantages:
VTEPs can be automatically discovered and VXLAN tunnels can be automatically established, simplifying network deployment and expansion.
EVPN can advertise both Layer 2 MAC address information and Layer 3 routing information.
Flooding traffic is reduced on the network.
Watching Videos to Learn About EVPN
The EVPN Feature Introduction 1 for CloudEngine Series Switches video shows how to use BGP EVPN to establish VXLAN tunnels and forward packets in a scenario where hosts on the same network segment communicate with each other at Layer 2.
The EVPN Feature Introduction 2 for CloudEngine Series Switches video shows how to use BGP EVPN to establish VXLAN tunnels and forward packets in a scenario where hosts on different network segments communicate with each other at Layer 3.
