Quanta Cloud Technology QuantaMesh QNOS5, Configuration Manual

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9.6.2.3. VTEP Nex-hop Resolution
A remote VTEP is considered reachable if the gateway has a non-default route to the VTEP's IP address. The
VXLAN application determines the reachability of the VTEP's address and registers with the routing table
manager for changes in the route to that IP address. When there is a route to the VTEP, the VXLAN application
copies the next hops of the best route and uses them as the next hop for the packets forwarded to that
VTEP. The VXLAN application creates a tunnel in the hardware for each reachable VTEP. The gateway may
use multiple next hops to a VTEP, hashing a given flow to an individual next hop as is done in layer-3 routing.
The number of next hops to a VTEP and, thus, the number of next hops for a tunnel, is limited only by the
ECMP limit of the platform (or the active SDM template).
The VXLAN application registers with the routing table manager for next-hop resolution changes for each
VTEP's remote IP address. When VXLAN receives a next-hop resolution change event, it queries the routing
table manager for the new best route and updates the set of next hops to the VTEP. If the VTEP is unreachable,
VXLAN deletes the corresponding tunnel in the hardware.
A VTEP cannot be resolved by a default route. The presence of a default route does not provide any
confidence that the VTEP is actually reachable.
9.6.2.4. VXLAN UDP Destination Port
The VXLAN standard defines 4789 as the standard UDP destination port to be used for encapsulation and
termination. Switches that supported earlier draft versions used custom defined UDP port numbers. To be
compatible with those switches, VXLAN supports switch-level VXLAN UDP destination port configuration. By
default, the VXLAN UDP destination port is set to 4789 on the switch. The switch terminates incoming VXLAN
traffic when the UDP destination port in the VXLAN header matches 4789 and encapsulates VXLAN tenant
traffic by putting 4789 in the UDP destination port field in the VXLAN frame.
Users can modify how VXLANs are terminated or encapsulated by changing the default VXLAN UDP
destination port configuration on the switch. When the VXLAN UDP destination port is modified, all existing
tunnels are modified in the hardware to encapsulate using new VXLAN UDP destination port information.
The switch is also configured to terminate VXLAN traffic using the new configuration. There is no or very
minimal traffic disruption during this operation.
Note: By default, the switch is configured to generate a source port (in the outer UDP header of the
VXLAN frame) that is a hash of the inner Ethernet frame's headers. This is to enable a level of entropy for
ECMP/load balancing of the VM to VM traffic across the VXLAN overlay.
9.6.2.5. Tunnels
The VXLAN application creates a tunnel in hardware for each configured and reachable remote VTEP. To
create a tunnel in hardware, the application must provide the following tunnel parameters:

A local IP address. This is the source IP address configured for the VXLAN. The hardware sets
the source IP address of the outer IPv4 header to this value.

The remote IP address. This is the IP address of the VTEP. The hardware sets the destination
IP address of the outer IPv4 header to this value.