BGP EVPN Part II: Network Virtualization Overlay with BGP EVPN and VXLAN - Introduction

In Figure 1-1, we have a routed 3-stage Clos Fabric, where all Inter-Switch links are routed point-to-point layer-3 connections. As explained in previous sections, a switched layer-2 network with an STP control plane allows only one active path per VLAN/Instance and VLAN-based traffic load sharing. Due to the Equal Cost Multi-Path (ECMP) supported by routing protocols, a routed Clos Fabric enables flow-based traffic load balancing using all links from the ingress leaf via the spine layer down to the egress leaf. The convergence time for routing protocols is faster and less disruptive than STP topology change. Besides, a routed Clos Fabric architecture allows horizontal bandwidth scaling. We can increase the overall bandwidth capacity between switches, by adding a new spine switch. Dynamic routing protocols allow standalone and virtualized devices lossless In-Service Software Update (ISSU) by advertising infinite metrics or withdrawing all advertised routes.

But how do we stretch layer-2 segments over layer-3 infrastructure in a Multipoint-to-Multipoint manner, allowing tenant isolation and routing between segments? The answer relies on the Network Virtualization Overlay (NVO3) framework. 

BGP EVPN, as an NVO3 control plane protocol, uses EVPN Route Types (RT) in update messages for identifying the type of advertised EVPN NLRIs (Network Layer Reachability Information). Besides publishing prefix information with RT-5 (IP Prefix Route), BGP EVPN uses RT-2 (MAC-IP advertisement) for publishing hosts’ MAC/IP addresses NLRI. Among these two fundamental route types, BGP EVPN can create a shared delivery tree for layer-2 Broadcast traffic, such as ARP Request messages, without using a Multicast-enabled underlay network. Besides, BGP EVPN allows us to implement a Tenant Routed Multicast (TRM) solution. We can use a vPC for device multihoming, but BGP EVPN has a built-in ESI multihoming option utilizing RT-1 (Ethernet AD Route) and RT-4 (Ethernet Segment Route). This solution uses a proactive control plane learning, where Leaf switches publish reachability information when a hos joins the network.

Virtual Extensible LAN (VXLAN) encapsulation allows switches to add a Layer-2 Virtual Network Identifier (L2VNI) for Intra-VLAN traffic and L3VNI for Tenant-specific/VRF Inter-VLAN connections. The Generic Protocol Extension for VXLAN (VXLAN-GPE) enables leaf switches to add a Group Policy to data packets. 

Finally, adding a new Layer-2 segment to a BGP EVPN fabric requires configuration only in leaf switches. We don’t have to touch Inter-Switch links or spine switches, like we must do in Layer-2 switched infrastructure. 

In the upcoming chapter, we delve deeper into the implementation and advantages of the BGP EVPN with VXLAN data center fabric solution.

Figure 1-1: Routed 3-Stage Clos Fabric with BGP EVPN and VXLAN.

VXLAN Part XV: Analysis of the BGP EVPN Control Plane Operation

Document Status: Unfinished
Edited: Monday, 7 January 2019

This chapter covers the following topics:

MAC address learning process (Intra-VNI switching): This section describes how the local VTEP switch learns the MAC addresses of its’ directly connected hosts from the ingress frame and installs the information into the MAC VRF in Layer 2 Routing Information Base (L2RIB) by the L2 forwarding component (L2FWDER). This section also shows how the local VTEP switch advertises the MAC address information to the remote VTEP switch by using BGP EVPN Route Type 2 advertisement (MAC Advertisement Route) and how the Remote VTEP switch installs information into MAC VRF in L2RIB and from there into MAC address table. Intra-L2VNI (Switching) Data Plane operation is explained at the end of the section with various frame capture examples. The white “MAC line” represents these processes in figure 7-1.

MAC-IP address learning process (ARP for Intra-VNI switching and ): This section gives a detailed description how the local VTEP switch learns the IP addresses of its’ locally connected hosts from ARP messages generated by the host and how the Host Mobility Manager component (HMM) installs the information into the IP VRF. This section also shows how the local VTEP switch advertises the IP address information to the remote VTEP switch by using BGP EVPN Route Type 2 (MAC Advertisement Route) advertisement and how the remote VTEP switch installs this information into IP VRF in L2RIB as well as into L3RIB of VRF TENANT77. In addition, this section explains how the ARP Suppression mechanism use MAC-IP binding information to reduce BUM (Broadcast, Unknown Unicast, and Multicast) traffic in VXLAN Fabric. The grey “IP line” represents these processes in figure 7-1.

Prefix advertisement: This section covers how the local VTEP switch redistributes its Anycast Gateway (AGW) subnets into BGP and advertises this information to the remote VTEP switch by using BGP EVPN Route Type 5 (IP Prefix Route) advertisement. This section also explains how the information is used to discover silent hosts. This section also describes how the remote VTEP installs the route from the BGP into local L3RIB. The black “Prefix line” represents these processes in figure 7-1.

Figure 1-1: BGP EVPN Control Plane Operational Overview.

VXLAN Part XIV: Control Plane Operation in BGP EVPN VXLAN Fabric

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"Virtual Extensible LAN VXLAN - A Practical guide to VXLAN Solution Part 1. (373 pages)

The focus of this post is a Control Plane operation in VXLAN fabric. First, we are going to see how the local switch Leaf-101 learns and installs the MAC address and IP address information of host Beef into databases. Then, we are going to see how Leaf-101 advertises the information to remote Leaf-102 by using BGP EVPN. After that, we are going to see how remote switch Leaf-102 receives the BGP EVPN Update and import routes into MAC-VRF and from there into databases. Note that in Leaf-101 the VLAN 10 is attached to VNI 10000 while VLAN 20 is attached to the same vn-segment in Leaf-102.

Figure 14-1: IP- and MAC addressing and VLAN-to-VN-segment mapping.