Layer 3 External Connectivity with VRF-Lite Using VRF allows for the use of multiple routing tables that are independent and isolated. VRF-Lite is a mechanism to extend the tenant Layer 3 VRF information beyond the BGP EVPN VXLAN Fabric. External connectivity with VRF-Lite or VRF handoff involves a two-box approach where the border node and the edge router are physically independent devices. With VRF-Lite handoff, the BGP EVPN VXLAN fabric extends the connectivity for different tenants externally on a hop-by-hop basis. Once the border node learns external routes from the edge router, it advertises the prefixes inside the BGP EVPN VXLAN fabric as EVPN type 5 routes.
This information is distributed to all the other VTEPs in the network. The border node also advertises EVPN routes to the external edge router. It sends the EVPN routes learned from the Layer 2 VPN EVPN address family to the IPv4 or IPv6 unicast address family. Layer 3 Multicast External Connectivity with MPLS Layer 3 VPN Layer 3 external connectivity with an MPLS Layer 3 VPN network or MPLS handoff uses a single-box approach. The single-box approach combines the functionalities of an EVPN VXLAN border node and an MPLS PE router into a single physical device. The device is also known as a border PE node.
The border PE node reoriginates IP prefixes from the EVPN address family of the BGP EVPN VXLAN fabric to the VPNv4 address family of the MPLS network. Likewise, the border PE node performs the corresponding function in the reverse direction. eBGP peering is necessary between the border PE node and the MPLS PE devices to ensure the connectivity. MPLS handoff allows scalability for EVPN VXLAN networks that have a large number of tenants or VRFs. Scalability is not possible with VRF-Lite handoff. In every VRF on a border VTEP, there are two sets of manually configured import and export route targets.
The first set of import and export route targets is associated with the BGP neighbor in the BGP EVPN VXLAN fabric. This BGP neighbor uses the EVPN address family to exchange Layer 3 information. The second set of import and export route targets is associated with the BGP neighbor in the Layer 3 VPN network. This BGP neighbor uses either VPNv4 or VPNv6 unicast address families to exchange Layer 3 information. The separation of route targets allows you to configure both sets of route targets independently. In this way, a border VTEP in an EVPN VXLAN network effectively stitches the two sets of route targets.
The route targets associated with the BGP neighbor in the Layer 3 VPN network are known as normal route targets. The route targets associated with the BGP neighbor in the BGP EVPN VXLAN fabric are known as stitching route targets. External Connectivity with Layer 2 Networks Layer 2 external connectivity or handoff for an EVPN VXLAN network extends the Layer 2 domain outside of the network. BGP EVPN VXLAN fabric supports Layer 2 external connectivity with IEE 802.1Q, access, and VPLS over MPLS networks.
Layer 2 External connectivity with IEEE 802.1Q or Access Networks Layer 2 handoff to IEEE 802.1Q networks is achieved through a regular IEEE 802.1Q Trunk port configuration on the Switchport interfaces on the border nodes. You can also connect EVPN VXLAN networks to external access networks. The commonly deployed scenario has EVPN enabled at the distribution layer and has the access layer switches connected with IEEE 802.1Q Trunk encapsulation. The IEEE 802.1Q Layer 2 traffic that comes from the access layer switches is mapped to the corresponding VLAN. The border node then bridges the traffic towards the destination with VXLAN encapsulation.
The inner packet does not carry the IEEE 802.1Q tag. Instead, the VXLAN network identifier (VNI), which is the Layer 2 VNI in the VXLAN header, represents the broadcast Configuring EVPN VXLAN External Connectivity External Connectivity with Layer 2 Networks Configuring EVPN VXLAN External Connectivity 5