Hello aspirant, first of all I would like to congratulate you for deciding a career that you want to pursue in future as many students just go with the flow till colleges  and then realize their interests. IIT is not the only way to become a computer network analyst. For being a successful computer network analyst you need to get a bachelors degree from any good universities which may be IIT, NIT, IIIT, GFTI or even good private universities offer best learning environment. IITs are the best public engineering institutes of India but they are not the only option.

Computer network analyst generally falls under IT branch but some colleges offer CSE specialization with Network analysis. For admission in IIT,NIT,IIIT or GFTI you have to qualify JEE mains exam and for IIT JEE Advanced exam.  After getting a bachelor's degree from a good college you can obtain certification like CCNA which is Cisco Certified Network Associate . Get a lot of work experience and learn new technologies.

BEST OF LUCK!!