Cisco Nexus 7000 Series Configuration Manual page 24

VXLAN Layer 3 Gateway
information to route the packet (to the destination subnet/VNI), but the actual remote switch to which
the packet needs to be forwarded is resolved at the Layer 2 level, which is done via data plane learning.
Figure 2: Layer 2 Gateway Packet Header (VM31-PII)
Figure 3: Layer 3 Gateway Packet Header (VM31-P12)
For example, in the above diagram the packets from VM31 (1.1.1.x) to P12 (2.2.2.x) are resolved at the Layer
3 level to go to SVI_VNI_20.20. After the routing, the destination VTEP, that is responsible for the destination
host, is identified at the Layer 2 level. There are two cases to consider here:
1 If the switch that runs the Layer 3 gateway functionality does not run Layer 2 gateway functionality, that
is, participates in the data plane learning, it has to flood the post-routed packet to all Layer 2 gateways
through the multicast tree.
2 If the switch runs Layer 3 gateway and Layer 2 gateway functionality, the switch can resolve the destination
VTEP at the Layer 2 level, and can forward the packet to the correct VTEP by itself.
Since Layer 2 gateway and Layer 3 gateway functionalities are tightly integrated from the configuration
perspective (Layer 3 gateway is achieved by configuring the BDIs for bridge-domains corresponding to the
VNIs), case (1) will not be applicable in the Cisco Nexus 7000, and only case (2) is supported.
Cisco Nexus 7000 Series NX-OS VXLAN Configuration Guide
16
Configuring VXLAN Flood and Learn