IGI takes the core software from three main release distributions gLite 3.2, EMI and UMD.
IGI release is created starting from the main release (glite 3.2, EMI, UMD) and for some profiles are done some cutomization to simplify the installation or to adding some more feature useful for the IGI sites.
IGI deals all the software from two mirrors, the main in Padova and the backup in Bologna. Have a look to Repositoy Specitication