This post shows how to connect an external network to our existing VXLAN fabric. From the two models, Border Leaf and Border Spine, I am going to use Border Leaf model since I do not want to install additional services to the Spine switches, which already hosts both Multicast Rendezvous Point (RP) and BGP Route Reflector (BGP RR). We could, of course, implement Border to Spine switches without having any performance issue, but then the Spine switches become VTEP switches, which means that they will do a VXLAN encapsulation and decapsulation. Keep it in mind that if we scale out the Spine layer by adding a new Spine switch, we also need to scale out the external connection. With the Border Leaf solutions, we get a dedicated border zone.
I am using full-mesh BGP model instead of a U-shaped model for a couple of reasons, it is the most resilient option, there will be no black holing in event of one link failure and there is no need for iBGP peering between Border Leaf switches.
Figure 8-1 shows the topology which we are going to build.
Figure 8-1: VXLAN Fabric external connection basic setup.
