VXLAN Gateways

VXLAN gateways are used to connect VXLAN and classic VLAN segments to create a common forwarding domain so that tenant devices can reside in both environments. The types of VXLAN gateways are

Layer 2 Gateway: A Layer 2 VXLAN gateway is a device that encapsulates a classical Ethernet (CE) frame into a VXLAN frame and decapsulates a VXLAN frame into a CE frame. A gateway device transparently provides VXLAN benefits to a device that does not support VXLAN; that device could be a physical host or a virtual machine. The physical hosts or VMs are completely unaware of the VXLAN encapsulation.

VXLAN Layer 3 Gateway: Similar to traditional routing between different VLANs, a VXLAN router is required for communication between devices that are in different VXLAN segments. The VXLAN router translates frames from one VNI to another. Depending on the source and destination, this process might require decapsulation and re-encapsulation of a frame. The Cisco Nexus device supports all combinations of decapsulation, route, and encapsulation. The routing can also be done across native Layer 3 interfaces and VXLAN segments.

You can enable VXLAN routing at the aggregation layer or on Cisco Nexus device aggregation nodes. The spine forwards only IP-based traffic and ignores the encapsulated packets. To help scaling, a few leaf nodes (a pair of border leaves) perform routing between VNIs. A set of VNIs can be grouped into a virtual routing and forwarding (VRF) instance (tenant VRF) to enable routing among those VNIs. If routing must be enabled among a large number of VNIs, you might need to split the VNIs between several VXLAN routers. Each router is responsible for a set of VNIs and a respective subnet. Redundancy is achieved with FHRP.