SCENARIO: Host A communicating internally with Host B
Host A connects to SW1
SW1 caches the location of Host A
SW1 sends a map-register message to the control plane node.
Control plane node creates an EID (Endpoint Identier) to RLOC (Remote Location) mapping. For clarity – RLOC’s are loopback addresses on the fabric edge nodes.
Host B joins SW2 repeating the process above.
Host A wants to communicate with Host B
SW1 doesn’t know where Host B is connected so sents a map-request to the control plane node.
The control plane node notifies SW2 (where host B is connected) that SW1 needs to know where it Host B is and SW2 replies directly to host A with a map-reply.
SW1 caches the response in its map database.
The packet is then re-encapsulated in with the RLOC of SW1 as the source and RLOC of SW2 as the destination. The SGT and VNID are also encapsulated. This allows routing through the underlay network.
SW2 decapsulates the packet, looks at the tags and decides using the policy whether or not to deliver the packet to Host B.
SCENARIO: Host A connecting to the Internet
Host A is connected to the fabric via SW1 as per the example above.
Host A sends packet for Internet destination.
SW1 receives packet but has no cached entry for the destination.
SW1 sends a map-request to the control plane node.
As the control plane doesn’t know about the destination address (it’s on the Internet), it replies to the RLOC of the External Border Node.
The same packet encapsulation process as above occurs.