Working through an initial NSX deployment and trying to setup the VXLAN transport configuration on our clusters. We've left the MTU setting at 1600, but whenever we click save and view the final configuration it always reverts up to 9000. This happens on multiple clusters and distributed switches. The DVS that the VXLAN will use has an MTU of 9000 - I'm not sure if that's where it is pulling it from, but we can't change that because there are other non-VXLAN port groups on the DVS that need to be at 9000.
Our interconnect between sites only support up to 4000 MTU, so we are safely above the 1600 limit and we don't plan to have any VMs in VXLAN segments using above 1500 MTU, but I don't want to risk issues with a 9000 MTU set on VXLAN.
According to VMware support, this is expected behavior if the MTU of the parent DVS is 9000 and the VXLAN traffic will still be limited to 1600 regardless.