BGP EVPN VXLAN Inter VNI Routing - Control Plane Learning

Host Route Advertisement: Inter-VNI Routing ( L3VNI)

In this section , we will see how host routes are imported in to L3RIB and how this information is used for Inter-VNI Routing .

Below figure explains the method, how Host route propagation happens over VXLAN fabric.

In this section, we will learn this propagation under various Phases. Let’s discuss all phases one by one.

Phase 1: Host Route in local RIB:

In previous section , we have seen how MAC-IP binding information installed in to ARP table by local VTEP and how HMM component installs the information in to L2RIB and same from ARP table to L3RIB.

This information can be verified by checking the RIB of TENANT55 VRF in local VTEP on Leaf-101. The route is learned from VLAN 10 and is installed into RIB by HMM.

Phase 2: Host Route Process on local VTEP.

In previous section , we have also covered , How MAC-IP information is sent from l2RIB to Loc-RIB and from there it is sent to Adj-RIB-Out , where it is advertised as an BGP EVPN Route type 2 update to remote VTEP switches. 

Phase 3: Host Route on remote VTEP by BGP Process

BGP EVPN Route type 2 Update concerning the MAC-IP NLRI of Beef includes also Route Target 65000:10055 (L3VNI). The received NLRI information is sent through the Import Policy Engine (import is based on RT 65000:10055) and the Decision process into Loc-RIB as an L3VNI entry. During the Input Policy processing, the original RD 192.168.55.101:32777 is changes to VRF TENANT55 specific RD 192.168.77.102:3 (3 = VRF Id of VRF TENANT55). RD is used for the differentiated overlapping IP address in different VRFs.

Below figure shows the BGP table of Leaf-102. The first highlighted portion is the original, received NLRI in Adj-RIB-In. The second highlighted portion is the same update imported into Loc-RIB. The import is based on the RT 65000:10055 defined under VRF Context. The RD is changed from 192.168.55.101:32777 to 192.168.55.102:3.

Phase 4: Installing Host Route in to remote VTEP RIB:

Now Route is installed in to L3RIB from BGP Loc-RIB, which includes information about Next-HOP Ip address and tunnel-id , encapsulation type: VXLAN , segment id , Route Source( BGP).