Info taken from histories by Herodotus, Amonios, Strabus and more modern historians Will durant”age of Faith-“our oriental Heritage” and also H.G. Wells the “outline of history”.
1-The Scythians or Scyths (in farsi Sag Zian or in old pahlavi Saka)were a nation of horse-riding nomadic pasturalists originally of Aryan Iranian stock or proto indo-european. Herodotus (c. 440 BCE) in his Histories wrote about them and more studies are done archaeologically from the exquisite goldwork found in Scythian burial mounds in Ukraine and Southern Russia.They were great worriers who were ancient cousins to Persians & Medes .Majority of their tribes lived on caucasian mountains and did raid far into hakhamaneshi IranKurdistan.King Darius went after them with huge army & chased them all the way to western Ukraine but couldn,t defeat them.They finally joined the Franks tribes in central europe and were dissolved into them as Saxons.remnants of them still can be seen in Lurestan,hamadan and Azarbaijan.
2-Sarmatians: A northern Iranian tribe who were chased by huns in 400AD to southern Scandinavia(todays Belarus, Finland,Norway):A popular belief (Sarmatism) in the Polish-Lithuanian Commonwealth held that the nobility were direct descendants of the Indo Iranian Sarmatians.although the considerable influence of the Sarmatian language and Indo-Iranian religion on the proto-Slavs now seems beyond doubt.
The Sarmatians, Sarmatae or Sauromatae (Old Iranian Sarumatah ‘archer’) were a people originally of Iranian stock from Iran. Mentioned by classical authors, they migrated from Central Asia to the Ural Mountains around 5th century B.C. and eventually settled in most of southern European Russia, Ukraine, and the eastern Balkans.forefathers to todays Serbs & Croats.The old name of Paraćin (Paratjin) in Serbia was Sarmatae.no wonder that there are over 1000 same root words in todays Persian & Serbo Croate language.
Around the year 100 BC, Sarmatian land ranged from Barents Sea or Baltic Sea (“Oceanus Sarmaticus”) to tributary of Vistula River, to the Carpathian Mountains, to the mouth of the Danube, then eastward along the northern coast of the Black Sea, across the Caucasus to the Caspian Sea and north along the Volga up to the polar circle in southern Scandinevia.
3-Alans:The Alans or Alani (occasionally but more rarely termed Alauni or Halani) were an Iranian nomadic group close to the Sarmatian people, warlike nomadic pastoralists of varied backgrounds, who spoke an Irania language and to a large extent shared a common culture with Iranian Aryan Races. After being overrun by Huns they moved from their northern Iranian towns and gradualy over 20 years around 390AD joined the Germanic tribes of Vandals and Sueves in their invasion of Roman Gaul. Gregory of Tours mentions in his Liber historia Francorum (“The book of the history of the Franks”) that the Alan king Respendial saved the day for the Vandals in an armed encounter with the Franks at the crossing of the Rhine on December 31, 406). According to Gregory, another group of Alans, led by Goar, crossed the Rhine at the same time, but immediately joined the Romans and settled in Gaul.The Alans were also known over the course of their history by another group of related names including the variations Asi, As, and Os (Hungarian Jász, Russian Jasy, Georgian Osi). It is this name which is the root of the modern Ossetian and part of southern Hungary.
there are some other indo european tribes of Iran which is out of the range of this short article :Dacians…Iberians,,Ostrogoths or East Germanic tribes(half brothers to Parthians AKA Ashkanis )