See this depends on the branch you are applying for, plus the GATE score you are using. GATE score as you know is valid for three years so wherever the IITs feel necessary, they hold a personal interview or a test. Most of the times, the admissions are through GATE only. For this kind of informatio, you will have to narrow down the IITs you are interested in, specialization you want to pursue and then check the respecive IIT portal.