External Connection with VXLAN Fabric

External Connection with VXLAN Fabric

External Connection can be terminated either to Spine or Leaf Switches, but preference is always given to connect the External Connection to Border Switches, because Spine Switches already host both Multicast RP and BGP Route Reflector.

In this chapter, we will use BGP Full mesh with External Router, to provide resiliency in topology and also to avoid traffic blackholing in event of One Link failure. 

Below the reference topology, for VXLAN Fabric External Connection.

Now lets see the configuration part Step by Step for above topology.

Step 1: eBGP Configuration between Leaf-102 and EXT-Ro01

Both Interface of EXT-Ro01 are in VRF TENENT55 and an eBGP peering has been established via these interfaces. VXLAN fabric belongs to BGP AS 65000 and EXTRo01 belongs to BGP AS 64555.

Below figure explains the VXLAN fabric External Connection topology.

Below is the configuration of Border leaf-102.

Example below shows the VRF TENENT55 specific configuration on EXT-Ro01 . currently on routing information exchange between VXLAN fabric and External network

Now lets understand the Routing Advertisement.

EXT-Ro01 starts advertising network 172.16.10.0/24 to its eBGP Peer Leaf-102. And it generates the BGP updates message , as shown in below figure .

BGP Update message includes the path attributes like : Next_Hop , NLRI , AS_Path.

When Border Leaf-102 receives the update , It creates two BGP Routing table entries, One under IPV4 Unicast AFI and other one under L2VPN EVPN AFI . Since BGP update about 172.16.10.0/24 was received by interface that belongs to VRF TENENT55 , Border Leaf-102 attaches RT 65000:10055 to BGP table entry .