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Traditionally, MAC address learning in VXLANs is achieved through flooding. In EVPN where BGP is used as the control plane for VXLANs, the problem of flooding can be eliminated through sending EVPN Type-2 advertisement between VTEPs assuming the ARP and ND suppression is enabled. In Figure 2, when Host 1 is first plugged into R1, Host 1 will start sending ARP and other basic networking traffic like DHCP. When R1 receives a packet from Host 1 for the first time, it will record its MAC address in its local MAC address table. Also, R1 will advertise an EVPN Type-2 route to R2. The route includes the local EVPN instance of R1, the VTEP IP address, the Host 1 MAC address and the L2VNI.
Upon recieving receiving the EVPN Type-2 route from R1, R2 learns the MAC address of Host 1. To accept this route, R2 needs to determine if the Import Route Target (IRT) configured on R2 matches the Export Route Target (ERT)
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. RT is sent as the BGP Extended Community attribute. In this case the IRT and ERT match hence the route is accepted and the MAC address of Host 1 is learned.
Figure 2. MAC Learning and Packet Forwarding
Packet Forwarding Process
In the case of packet forwarding within the same subnet as depicted in Figure 2
Verifying Configuration
To check the BGP state and neighbor status on Router 2, we will run the run show bgp neighbor command.
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