Contents

EVPN overview·· 1

EVPN VXLAN· 1

EVPN benefits· 1

Layered transport network· 2

MP-BGP extension for EVPN· 2

RD and route target selection of BGP EVPN routes· 3

EVPN overview

Ethernet Virtual Private Network (EVPN) is a Layer 2 VPN technology that provides both Layer 2 and Layer 3 connectivity between distant network sites across an IP network. EVPN uses MP-BGP in the control plane and Virtual eXtensible LAN (VXLAN) in the data plane. EVPN is typically used in data centers for multitenant services.

EVPN VXLAN

As shown in Figure 1, EVPN VXLAN uses the VXLAN technology for traffic forwarding in the data plane. The transport edge devices assign VMs to different VXLANs, and then forward traffic at Layer 2 between sites for VMs by using VXLAN tunnels. The transport edge devices are VXLAN tunnel endpoints (VTEPs). All EVPN VXLAN processing is performed on VTEPs

To provide Layer 3 connectivity between subnets of a tenant and between the EVPN VXLAN network and external networks, you can deploy EVPN gateways.

For more information about EVPN VXLAN, see "Configuring EVPN VXLAN."

Figure 1 EVPN VXLAN network model

EVPN benefits

EVPN provides the following benefits:

·     Configuration automation—MP-BGP automates VTEP discovery, VXLAN tunnel establishment, and VXLAN tunnel assignment to ease deployment.

·     Separation of the control plane and the data plane—EVPN uses MP-BGP to advertise host reachability information in the control plane and uses VXLAN to forward traffic in the data plane.

·     Integrated routing and bridging (IRB)—MP-BGP advertises both Layer 2 and Layer 3 host reachability information to provide optimal forwarding paths and minimize flooding in an EVPN VXLAN network.

·     Point-to-point and point-to-multipoint connection—Layer 2 frames are transmitted transparently across the IP transport network between sites after they are encapsulated into VXLAN packets.

Layered transport network

As shown in Figure 2, typically the EVPN transport network uses a layered structure. On the transport network, leaf nodes act as VTEPs to provide VXLAN services, and spine nodes perform forwarding for VXLAN traffic based on the outer IP header. If all VTEPs and transport network devices of an EVPN network belong to the same AS, the spine nodes can act as route reflectors (RRs) to reflect routes between the VTEPs. In this scenario, the spine nodes advertise and receive BGP EVPN routes, but do not perform VXLAN encapsulation and de-encapsulation.

Figure 2 Layered transport network

MP-BGP extension for EVPN

To support EVPN, MP-BGP introduces the EVPN subsequent address family under the L2VPN address family and the following network layer reachability information (BGP EVPN routes):

·     Ethernet auto-discovery route—Advertises ES information in multihomed sites.

·     MAC/IP advertisement route—Advertises MAC reachability information and host route information (host ARP or ND information).

·     Inclusive multicast Ethernet tag (IMET) route—Advertises VTEP and VXLAN mappings for automating VTEP discovery, VXLAN tunnel establishment, and VXLAN tunnel assignment in an EVPN VXLAN network.

·     Ethernet segment route—Advertises ES and VTEP mappings.

·     IP prefix advertisement route—Advertises BGP IPv4 or IPv6 unicast routes as IP prefixes.

·     Selective multicast Ethernet tag (SMET) route—Advertises IGMP multicast group information among VTEPs in an EVPN network. A VTEP advertises an SMET route only when receiving a membership report for an IGMP multicast group for the first time. The VTEP does not advertise an SMET route if subsequent membership reports for the multicast group use the same IGMP version as the first membership report.

·     IGMP join synch route—Advertises IGMP membership reports among redundant VTEPs for an ES.

·     IGMP leave synch route—Advertises IGMP leave group messages for withdrawal of IGMP join synch routes among redundant VTEPs for an ES.

MP-BGP uses the route distinguisher (RD) field to differentiate BGP EVPN routes of different VSIs and uses route targets to control the advertisement and acceptance of BGP EVPN routes. MP-BGP supports the following types of route targets:

·     Export target—A VTEP sets the export targets for BGP EVPN routes learned from the local site before advertising them to remote VTEPs.

·     Import target—A VTEP checks the export targets of BGP EVPN routes received from remote VTEPs. The VTEP imports the BGP EVPN routes only when their export targets match the local import targets.

RD and route target selection of BGP EVPN routes

As shown in Table 1, you can configure RDs and route targets for BGP EVPN routes in multiple views.

Table 1 Supported views for RD and route target configuration

The device selects RDs and route targets for BGP EVPN routes by using the following rules:

·     Ethernet auto-discovery routes—The device uses the RD and route targets configured in VSI EVPN instance view when advertising the routes. The device uses the route targets configured in VSI EVPN instance view when accepting the routes.

·     IMET routes and MAC/IP advertisement routes that contain only MAC addresses—The device uses the RD and route targets configured in VSI EVPN instance view when advertising. The device uses the route targets configured in VSI EVPN instance view when accepting the routes.

·     MAC/IP advertisement routes that contain ARP or ND information—The device uses the following settings when advertising the routes:

¡     RD and export route targets configured in VSI EVPN instance view.

¡     Export route targets configured for EVPN on a VPN instance or the public instance (VPN instance view, EVPN view of a VPN instance or the public instance, and public instance view).

The device uses the import route targets configured for EVPN on a VPN instance or the public instance when accepting the routes.

·     ES routes—The device uses the RD and export route targets configured in VSI EVPN instance view when advertising the routes. The device uses the import route targets configured in VSI EVPN instance view when accepting the routes.

·     IP prefix advertisement routes—The device uses the route targets configured for the IPv4 or IPv6 address family on a VPN instance or the public instance when advertising and accepting the routes.