According to the regulations of the Iranian Ministry of Foreign Affairs, a Tourist visa is issued for foreign nationals who are interested to travel to Iran individually or with a group for the purpose of visiting Iran, or their friends and relatives. This visa is issued for a maximum stay of 30 days with option of Extensions in Iran. The visa remains valid for a period of 3 months from the date of issue.
Depending to your nationality and the consulate which you refer, it is possible to submit your documents and receive a visa after some days without any reference from Iran. But it can be a time-consuming or even fruitless attempt, specially when you are applying out of your country. Most consulates need an authorization letter from the Ministry of Foreign Affairs in Tehran. Getting this authorization is the most important step in visa application and there is not much left when you have it. You will usually have your visa in 1 or 2 days, after having the authorization letter.