Do you pray Sunnah and Fard separately?

Ok, it is a bit complex for me. Suppose you are praying for Fajr and you have got 2 rakat sunnah and 2 fard. How do you pray them? All in one go or do you pray sunnah first by making Niyah and in the end you give salam left and right and then you stand up make a new niyah for praying fard? Thank you.