This section details the BGP EVPN VXLAN support for data center interconnect (DCI).
Data center Layer 2
interconnect between EVPN VXLAN and EVPN MPLS or VPLS is not supported. However, EVPN
VXLAN and VPLS can coexist on the router, although a given VLAN/BD should not be
extended into EVPN and be configured for VPLS.
The following sections address a variety of DCI interconnect scenarios.
Layer 2 and Layer 3 control-plane extension
In this scenario, VXLAN tunnels are extended by means of a border leaf instead of getting terminated. This extension is primarily the spine functionality being provided by the border leaf, except that the control and forwarding planes are extended over the WAN/core in the case of a border leaf.
Layer 2 handoff
In this scenario, VXLAN tunnels are terminated at the
border leaf, as shown in the following figure. Depending on the interconnect
technology being used between data centers extending over the WAN (such as VPLS,
VXLAN Layer 2 extension, or any other interconnect scheme), the border leaf bridges
the two domains through forwarding plane learning without any control plane
extension.
Layer 2 handoff-based
DCI
Layer 3 handoff
In the case of Layer 3, all VRFs in the data center are terminated
on the border leaf and traffic is routed towards the WAN, as shown in the following
figure. Similarly, Layer 3 traffic received from the WAN is routed and forwarded
over tunnels in the data center. Because Layer 3 routes across multiple VRFs can be
imported into a single (interconnecting) VRF, all possible VRFs in a given data
center do not have to be configured on the border leaf.
