VXLAN MTU Setting Reverts to 9000 on DVS Switch

[pbhite]

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.

[pbhite · Accepted solution]

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.

[padulka]

Hi pbhite, today to my customer I notice this strange behavior:

If I set MTU 1600 on DVS, configure the VXLAN on the hosts with value 1600 and after change on DVS the MTU to 9000, under VXLAN view configuration the MTU maintain 1600 value (figure 01)

If I set MTU 9000 on DVS, configure the VXLAN on the hosts with value 1600, under VXLAN view configuration the MTU change to 9000 value

But I don't know which is the impact to the environment and I don't know which is the better configuration.

The only certainty is I have to work with MTU 9000 because it's the phisycal hardware configuration.

Regards