I am not sure why this error happens. The error on a vMX happen
when a virtual network is extended into a vMX router(=gateway).
[edit groups __contrail__ interfaces lo0 unit 0 family inet] 'address xxx.xxx.xxx.xxx/32' identical address found on multiple private or public interfaces error: configuration check-out failed
On Contrail, I configured a bgp router and associated it to the vMX as a physical device. The IP address, xxx.xxx.xxx.xxx, is defined for a bgp router address and its router id. To make the router reachable to contrail, the IP address is set on ge-0/0/0.