Hello Jayprakash,

For admission in NIT, a candidate must appear for JEE Mains entrance exam. Unless you appear for the entrance exam you won't get be able to get admission in National Institute of Technology. The eligibility criteria for entrance exam is 12th with PCM as the subjects.

Apart from IIT and NIT, most colleges in India offer lateral entry for diploma students. These colleges do reserve some seats for lateral entry students. But, there is no direct exam to get admission in IIT/NIT after complete a diploma course.

Good luck!