1.The leaf and spine nodes set up full-mesh connections. At least two spine nodes need to be deployed on the network, which back up each other and implement load balancing. Forwarding paths are established between leaf nodes through Layer 3 routing. Normally, ECMP paths exist between leaf nodes. 2.The spine and leaf nodes all function as VTEPs. 3.A leaf node only completes Layer 2 traffic forwarding. It maps the VLAN tag of user packets to a VNI, encapsulates the packets in VXLAN packets, and forwards them to the destination node in the local bridge domain. 4.A spine node acts as a centralized Layer 3 gateway to decapsulate VXLAN packets and forward them based on Layer 3 routes, enabling communication between bridge domains on the network and communication with external networks.
BGP EVPN acts as the VXLAN control plane to provide the following functions:
packet format
n DA: specifies the destination MAC address of the outer packet. The value is the MAC address of the next-hop router in unicast forwarding, and is a multicast MAC address in multicast replication.
n SA: specifies the source MAC address of the outer packet. The value is the MAC address of each routing device that sends the VXLAN packet.
n DIP: specifies the IP address of the destination NVE.
n SIP: specifies the IP address of the source NVE.
n UDP Dest Port: specifies the destination UDP port number reserved for VXLAN. The default value is 4789.
n UDP Source Port: The value is dynamically generated based on the hash result of data flows.
n VXLAN I flag: The value must be set to 1, indicating that the VNI field is valid.
n VXLAN VNI: is a 24-bit value that identifies virtual networks. The maximum value is 16M.
n Original Ethernet Frame: As recommended in the standard, the VLAN tag of the original packet is removed after VXLAN encapsulation. Even if the VLAN tag is not removed, the egress NVE forwards the packet based on only the VNI (the VLAN of the original packet is ignored).