I'm not informed about Russia's relationship to Iran. What is Russia's strategic interest (dependency?) in Iran?
I'm not an expert either, and I asked the same question about China and Iran. Certainly they couldn't care less about Iran, right? Indeed, doesn't Iran's Islamic militancy encourage seperatists in both Russia and China??
I think it comes down to 1) basic Anti-Americanism and fear of US hegemony. 2) "the USA's loss is my gain" sort of thinking 3) fear that any change in Iran's Gov't will put them into a US "orbit." 4) need for "independent" energy suppliers able to poke the West in the eye.
Iran is right across the Caspian Sea from Russia and thus in its backyard. There is a lot of trade between the two countries.
Attacking Iran to Russia might be analogous to Russia attacking Mexico...
I think it's primarily military hardware and capital equipment for nuclear development. And, more than likely, nuclear delivery systems. Money and political influence. But, Russia doesn't have the military wherewith-all to project power beyond it's own borders. And, there's not an open land route between Russia and Iran available. I suppose Russia might work a deal with about three “stans” so to open a logistical land route. But, I don't think the “stans” are very fond of Russians. So, the only real threat at Russia's disposal is the nuclear option. And, I don't think even the Russians are that stupid.