It depends.
Prior to 1979 Iran was a wholly supported ally of the United States. It was specifically designated a U.S. special interest state and the government of Shah Reza Pahlavi was fully backed by the US with money, food and arms. After the fundamentalist revolution it was feared that Iran would become a Soviet bloc ally, or puppet state; this did not happen. Iran is almost as wary of Russia as it is the US. They do have a shared border and sea, and do have some trade agreements, yet they actually have had better relations with some European nations, including Germany and France.
Being as Iran does not want any part of the US or Russia dictating terms to them, it is unlikely that Russia would defend them against anything but a US invasion of Iran. That is not a highly likely proposition.
During the Iran - Iraq wars Russia actually provided some support to Iraq, while the US had made some backroom deals on both sides of the conflict (Iran-Contra scandal).
It doesn't look like Iran is trying to defend itself, Mahmoud Ahmadinejad is theatening to use nuclear weapons against Israel.
Russia sold weapons to Iran and Iraq.
No. While Iran has a maritime border with Russia, they are two distinct countries.
Russia is partly in Europe and partly in Asia. The Ural mountains divides the two. Iran is in Asia
Ayatollah Khomeini, He was also the head commander giving orders wheter to attack or defend cities.
Russia aka Russian Federation
The allies of are russia, iran, El Salvador, venezula, Bolivia, Brazil.
every country have the right to defend them self from evil why is USA not allowing Iran to do it? simply because Iran are EVIL
The Caspian Sea.
According to RT News as of 11/2013, Russia still supports Iran's nuclear program and is continuing to both broker a deal with their allies and provide support for the equipment they have already sold Iran. If I understand correctly, Russia sees cheap nuclear power as a good thing for Iran and doesn't believe that Iran has the intention to join the, "Nuclear Club".
It is highly unlikely that Iran would attack North Korea since the two countries are allies. It is possible, but still very unlikely, that Iran would attack South Korea. There would be no reason to justify it from an Iranian Foreign Policy Perspective.
Russia, Kazakhstan, Turkmenistan, Azerbaijan, and Iran border the Caspian Sea.