Dynamic Learning

Dynamic learning of remote MACs involves:
  • VTEP discovery—When a VNI is configured on a gateway, other VTEPs in the network would somehow have to discover the existence of the VTEP(s) this gateway is configured with.


    VTEP discovery is only supported using OSPF (Open Shortest Path First) extension. But not through receiving an encapsulated frame.
  • Remote MAC to IP—When an encapsulated frame is received from a remote VM, a VTEP needs adds an entry in its filtering database that binds the remote VM‘s MAC to the IP address of the remote VTEP
VXLAN supports standard and explicit-remotes flooding modes:
  • Explicit-remotes mode—VTEPs participating in a VNI are created statically either by the user or the controller.
  • Standard mode—OSPF is used to signal existence of other VTEPs. Traffic from unknown VTEPs is dropped and MAC to IP bindings are never learned.

Additionally the MAC-to-remote IP binding is added to the filtering database associated with the VNI‘s overlay network. The received encapsulated frame can either be addressed to the VTEP directly (in the case of known unicast) or to a multicast group that the VTEP joined.

Gateways will need to age remote VTEPs as done with MAC-to-IP bindings to ensure that the number of remote VTEPs does not remain monotonically non-decreasing over time.

A VM‘s MAC-to-IP binding may change if it has been migrated using Vmotion. As with FDB (forwarding database) learning, VTEPs need to dynamically detect these moves based on received traffic and update their filtering databases.