Currently there are two ways for the bootup script to determine which ethernet port is the LAN ( with the DUT's connected ) and which is WAN ( usually has access to google services via the internet )

1)  By puttin a mac address in a configuration file. ( used by moblab VM )
2)  By looking at device types and assuming the built in network is the WAN and the USB network is the LAN

Next Gen Moblab has 2 build in NIC's so these strategies need to be extended.

Next version will:

1) Check for the configuration file.
   if that is not successful then :
2) Check which interface has an IP address, WAN has IP LAN no IP
   if that is not successful then :
3) Check device types, USB still LAN ( Legacy )
   if that is not successful then :
4) Just pick one interface to be internal one to be external, this allow the device still to boot.