Requirements for Iran Tourist Visa:

Personal Information of your host in Iran
Office address and phone number of your host + home address and phone number of your    host  
Host’s colored scan of birth certificate 
Host’s ID number
Guest’s colored scan of passport
Address of guest’s accommodation
It takes 7 to 10 working days to receive visa confirmation number from the Ministry of Foreign Affairs. In case of Urgent Visa, it
 will reduce to 3 to 4 working days.
Iran Visa is valid for 3 months, enabling guests to stay in Iran for 30 days. In case of a request for an extended stay, a request for Visa extension application must be filled. 
Note that the Islamic Republic of Iran reserves the right, in its sole discretion, to provide or refuse to provide Visa for foreigners. 
Visitors to Iran with Iran Visa shall comply with all applicable laws and regulations in the Territory. 
The guest must specify where Iran Visa must be obtained.

: Visa transaction for foreigners at the airport

** Iran Tourist Visa can be obtained at the airport except for nationals of America, England, Canada, Colombia, Somalia, Bangladesh, India, Pakistan, Afghanistan, Jordan, and Iraq. The aforementioned nationals must collect their visa, prior to their visit to Iran, at Iran Consulate.  

Request for extended Iran visa:

Visa extension is not arranged by travel agencies or Passport Office. In order to obtain your visa, you shall go to Iranian Immigration and Passport Police Office in your town. Guest must refer to Iranian Immigration and Passport Police Office, bringing his/her passport with the company of his/her host, for visa stamping.
Notice: Arriving business passengers must have an invitation letter from their inviting company. Except for special occasions, extended Iran visa is usually not applied for tourists.