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>There seemed to be two ways to create a VM via cli:
>
>1) use neutron command to create a port first and then use nova command to attach the vm to that port(neutron port-create.. >followed by nova boot --nic port-id=)
>2)Just use nova command and a port will implicitly be created for you(nova boot --nic net-id=net-uuid).
>
>My question is : is #2 sufficient enough to cover all the scenarios?  In other words, if we are not allowed to use #1(can only use >#2 to create vm), would we miss anything?

You wouldn't be able to set the vnic_type of the port.
Setting vnic_type=direct is required to boot vm's with SRIOV ports.

Regards
Przemek