Unfortunately, IITs and NITs donot have any scope ofr Admission for diploma holders.

Candidates must have appeared for JEE main and Advanced, and should be from Scienece stream and have passed class 12th with Minimum 75% aggregate marks.
He/ She must have appeared for PCM Subjects.

This practically leaves out diploma holders.

However, one can get admissions directly into second year of Engineering with other colleges apart from IITs and NITs,  on basis diploma aggregate marks.
A minimum 50% marks is must.

Top colleges accepting Diploma holders are KJ Somaiaya, Thadomal shahani, Sikkim manipal, VIT Vellore, Etc.


You can get more information on official notification for diploma holders as per AICTE.

https://www.google.co.in/amp/s/engineering.careers360.com/aicte-informs-diploma-holders-need-not-appear-for-jee-main%3famp