Hi aspirant,
Diplomate of National Board (DNB) is a medical qualification awarded by the National Board of Examinations (NBE).Doctor of Medicine (MD) or Master's in Surgery (MS) is mostly limited to a post-graduation course in general medicine and surgery. DNB has limited seats all over as compared to MD. DNB are postgraduate or post-doctoral diplomas offered by the National Board of Examinations set up under the Ministry of Health and Family Welfare of Government of India. The three year training for DNB happens under a guide who may be in a public sector or private sector institution that has been accredited to conduct the training by the NBE. The NBE conducts the entrance and exit examinations after which the DNB is awarded. All DNB qualifications are recognised all over the country by the Medical Council of India.

As far as the official position of government of India is concerned ( via Gazette notifications) , DNB qualifications are equivalent to MD/MS in all respects. In practice however there is a tendancy to view DNB as being a rung below.

Hope this helps.