If you have 8.0 and above B.E or B.Tech Cgpa from any IIT of CFU you get admission in any IIT of NIT without entrance exams. One more you have to clear interview conducted by particular IIT in which you want to get admission.
You can also do PHD being sponsored from reputed industry like HAL and ISRO( seats are also reserved for this sponsorship)
You can also join research assistantship provided by IITs.
If you have teaching experience in well known college no need of GATE for phd or m.tech in iit.
But now if you are fresher or not an IITian you have to clear GATE compulsorily.