Learn return paths from multicast traffic
03RFC 7348 describes a data-plane learning scheme. A broadcast, multicast or unknown-destination Ethernet frame follows an IP multicast tree; received source addresses teach the return path.
A second example inserts the same inner MAC under VNI 200 with a different VTEP IP. The VNI 100 mapping remains 192.0.2.1; identical MAC text does not merge overlays.
Source for this drawing: RFC 7348 · Read RFC section 4.2 ↗
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A message needs an address.
Think of a packet as a small addressed envelope. Devices pass it onward; transport protocols decide what delivery promises an application gets.
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These pictures are analogies to help you learn. The linked RFC explains the actual rules.
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Learn (VNI, inner source MAC) → outer source VTEP IP, then use that mapping for a unicast reply.
- Management supplies the VNI-to-IP-multicast-group mapping. VTEPs join the relevant groups; the mapping shown here is an example, not a fixed address formula.
- An ARP request is an inner Ethernet broadcast. VXLAN carries it to the overlay’s IP multicast group. Unknown-MAC-destination and multicast inner frames use the multicast tree too.
- A receiving VTEP learns the inner source MAC’s association with the outer source VTEP IP. That knowledge allows the reply to use outer IP unicast. The inner ARP reply is still an Ethernet/ARP frame, not an IP packet.
- Other mapping-distribution schemes are possible, but this publication focuses on data-plane learning. The guide does not implement a later EVPN control plane.
The fictional mapping is VNI 100→239.1.1.100. The diagram includes a second VNI 100 receiver to show replication. Reusing the same MAC on VNI 200 must not overwrite VNI 100’s mapping. ARP is Address Resolution Protocol; optional background is RFC 826.
Read the RFC section ↗