Hello Sadhana. Thanks for contacting Careers360 and we hope we will be able to answer your query. 

Yes, all IITs have a same portal for its M. tech admissions, COAP. 

Candidates who have applied for M.Tech at various IITs can register for GATE COAP 2018 from April 6. The IITs have started the GATE Common Offer Acceptance Portal (COAP) from 2017 to facilitate students who have applied for the M.Tech admissions at the IITs. While candidates must apply for the respective IITs, the admission offers will be commonly available through GATE COAP.

Source:

• https://engineering.careers360.com/articles/gate-coap

Hope this helps you and all the best!