according to the VMware NSX Documentation, these are the three parameters that must match in
order to establish an OSPF neighbor relationship with an upstream router on a tier-0 gateway:
MTU of the Uplink: The maximum transmission unit (MTU) of the uplink interface must match the
MTU of the upstream router interface. Otherwise, OSPF packets may be fragmented or dropped,
causing neighbor adjacency issues.
Subnet mask: The subnet mask of the uplink interface must match the subnet mask of the upstream
router interface. Otherwise, OSPF packets may not reach the correct destination or be rejected by
the upstream router.
Area ID: The area ID of the uplink interface must match the area ID of the upstream router interface.
Otherwise, OSPF packets may be ignored or discarded by the upstream router.
https://www.computernetworkingnotes.com/ccna-study-guide/ospf-neighborship-condition-andrequirement.html
