Roughly speaking, nowadays, about 2% of Iran's population still follow the nomadic way of life. A century back it was about 25%, and so, the nomadic lifestyle is an integral part of Iranian culture. Unfortunately, these 2% folks are going to be extinct in some years. There are different tribes of nomads such as Qhashqaii, Bakhtiari and so on, who are scattered all over Iran; depending on the seasons (actually the weather) they regularly change their locations. But, most of the nomads are living in central Zagros (mountain ranges of Zagros) where nature feeds their livestock (livestock is the primary source of their income).
These are the places where I have met the nomads:
At the foot of Sahand mountain ( south of Tabriz)
Koohrang ( around Shahr-e Kord
Gachsaran (southwest of Shiraz)
Eqlid ( north of Shiraz)
Qaleh Babak ( northeast of Tabriz )
Nahawand (south of Hamadan)
Firuz Abad ( south of Shiraz).