BGP EVPN with VXLAN: Fabric Overview
Figure illustrates the simplified operation model of EVPN Fabric. At the bottom of the figure is four devices, Tenant Systems (TS), connected to the network. When speaking about TS, I am referring to physical or virtual hosts. Besides, The Tenant System can be a forwarding component attached to one or more Tenant-specific Virtual Networks. Examples of TS forwarding components include firewalls, load balancers, switches, and routers.
We have connected TS1 and TS2 to VLAN 10 and TS3-4 to VLAN 20. VLAN 10 is associated with EVPN Instance (EVI) 10010 and VLAN 20 to EVI 10020. Note that VLAN-Id is switch-specific, while EVI is Fabric-wide. Thus, subnet A can have VLAN-Id XX on one Leaf switch and VLAN-Id YY on another. However, we must map both VLAN XX and YY to the same EVPN Instance.
When a TS connected to the Fabric sends the first Ethernet frame, the Leaf switch stores the source MAC address in the MAC address table, where it is copied to the Layer 2 routing table (L2RIB) of the EVPN Instance. Then, the BGP process of the Leaf switch advertises the MAC address with its reachability information to its BGP EVPN peers, essentially the Spine switches. Continue reading