Hello Aspirant ,

Dnb means diplomate of national board as the dnb is the qualification awarded by the national board of examination has been equated with that of the post graduate and post doctral qualifications awarded by the universities for all the purposes including teaching posts also and yes in this application there are special categories like bc as if you per suppose belong to the obc category you belong to bc category only and you can go through bc category only and this dnb is prefered by several countries also and based on this application and any problems visit the official website mentioned below  and there you can know the complete details:

https://natboard.edu.in

And all the best for your future and i think my suggestions and knowledge may be helpful to you.

Thank you !!