now there is not any direct process for IIT and NIT you have to go through the normal process of appearing in JEE main and JEE advanced and once you qualify with a good rank then only you will be able to get admission into NIT then it is as is are the most premier Institute of India there is no any back door option.

for IIT there is an option called preparatory course which is for category students in that course the students who got very less marks but higher than others are selected for that course in that you will be given one year course and after that you will be enrolled into BTech