India has blocked at least 43,000 domains, according to a new research study that provides the clearest picture so far of the scale of DNS-based censorship in the country.

When users in India encounter a website that fails to load, they are typically not informed of the reason. Blocking orders are legally confidential, and Internet Service Providers (ISPs) are not obligated to disclose when or why access to a site has been restricted. This lack of transparency has made it difficult to measure the extent of online filtering.

A recent study titled “Poisoned Wells: Examining the Scale of DNS Censorship in India” offers new insight into the issue.

How the Study Was Conducted

Researcher Karan Saini, working with support from the Open Technology Fund and the Internet Governance Project at the Georgia Institute of Technology, conducted a large-scale technical analysis of domain accessibility in India.

The research involved querying 294 million registered domain names against DNS resolvers operated by six major Indian ISPs. In total, the study generated approximately 1.76 billion DNS queries.

DNS, or the Domain Name System, functions as the internet’s address directory. When a user types a website address, a DNS server translates that domain into a numeric IP address required to access the site. Since ISPs operate their own DNS servers, they can block access by returning incorrect or empty responses when a restricted domain is requested.

In such cases, the website appears to not exist, and users receive no explanation.

Key Findings

The study identified 43,083 blocked domains — six times more than the largest previous study had reported. Researchers caution that this number may still underestimate the total, as the study measured only DNS-based censorship. Other technical filtering methods could account for additional blocked sites.

One notable observation was the inconsistency in how ISPs implement blocking. Some domains under government namespaces such as gov.in and nic.in reportedly appeared on blocklists, suggesting that filtering decisions may not always be uniformly coordinated.

Why Earlier Research May Have Missed the Scale

To assess the broader impact, Saini cross-referenced the blocked domains with the Tranco ranking, a widely used list of the most visited websites globally.

The findings showed that only about 9,000 of the 43,083 blocked domains appeared among widely visited sites. This means roughly 78 percent of the blocked domains would not have been captured by traditional studies that rely on popularity-based lists.

Earlier research typically examined a few thousand domains drawn from curated or controversial website lists. By contrast, this study attempted to query nearly all registered domains, revealing a much wider scope of filtering.

Transparency and Public Awareness

According to Saini, the research was undertaken to address a fundamental gap in public knowledge. Because blocking orders in India are confidential and ISPs are not required to publish restriction lists, the true scale of internet filtering has remained unclear.

The study underscores the need for greater transparency in understanding how DNS-based censorship operates and how consistently it is applied across service providers.

While the findings focus specifically on DNS-level blocking, they represent one of the most comprehensive technical assessments of online filtering in India to date.