Mandatory DNS Blocking: What ISPs and Regulators in Latam Need to Understand
DNS blocking is one of the most commonly used tools by governments and regulators to restrict access to internet content: child pornography, illegal gambling, disinformation sites, malware infrastructure. The logic is simple: if you block the domain name at the resolver, you block access to the content.
But that simple logic hides technical consequences that ISPs, regulators, and security teams across Latin America need to understand before implementing — or complying with — DNS blocking mandates. Internet Society recently published an analysis that summarizes these consequences with clarity.
Why DNS Blocking Seems Like an Obvious Solution
From a non-technical regulator’s perspective, DNS blocking has obvious appeal:
- It’s fast: it can be deployed in hours by modifying the ISP’s resolver configuration
- It’s cheap: it doesn’t require deep packet inspection (DPI) or expensive infrastructure
- It’s visible: the regulator can verify that the ISP implemented the block simply by querying the domain
In Latam, DNS blocking mandates have become common: Chile, Brazil, Colombia, and Argentina all have legislation or regulatory precedents requiring ISPs to block specific domains across various content categories.
The Four Consequences the Regulator Doesn’t See
1. The Content Doesn’t Disappear — The Path Is Just Obscured
DNS blocking doesn’t remove content from the internet. The server still exists, the IP is still accessible, the content is still available. The only thing that changes is that the ISP’s resolver doesn’t respond to the query.
The practical result? Users who genuinely want to access the blocked content immediately adopt alternatives: VPNs, DNS over HTTPS (DoH) with external resolvers like 1.1.1.1 or 8.8.8.8, or simply changing DNS settings on their devices. The block is perfectly bypassable by anyone with access to Google.
Meanwhile, the ISP bears the operational and compliance cost of maintaining updated blocklists.
2. Inevitable Collateral Blocking
DNS resolves full domain names, not URLs or individual pages. When a domain is blocked, all content under that domain is blocked, including perfectly legal content.
Over-blocking cases are documented and recurring: shared hosting platforms where a blocked domain drags down thousands of innocent sites, CDNs whose domain shares infrastructure with problematic content, URL shortening services where a single blocked link affects the entire domain.
These collateral blocks have real consequences: businesses losing access to their own tools, citizens unable to reach legitimate services, companies unable to explain to their clients why their service doesn’t work at certain ISPs.
3. Interference with Security Protocols
This is the most concerning impact from a technical perspective: DNS blocking mandates can directly interfere with security mechanisms designed to protect users.
DNSSEC authenticates DNS responses. When a resolver modifies responses (as DNS blocking does), it can break the DNSSEC validation chain, leaving users without the protection that mechanism provides.
DNS over HTTPS (DoH) and DNS over TLS (DoT) encrypt DNS queries. Blocking mandates create regulatory pressure for ISPs to intercept or block these protocols — precisely the ones that offer the most privacy and security to end users.
RPKI and routing security: in environments where DNS is used as a routing verification component, resolver manipulation can have cascading effects.
4. Cross-Border Fragmentation
DNS is a global system. A block implemented in a Peruvian ISP’s resolvers does not affect a Chilean ISP’s resolvers — and vice versa. This creates inconsistencies where the same content is accessible in one jurisdiction and blocked in another, without the content itself having changed.
Internet Society notes that when these inconsistencies multiply, the cumulative result is the fragmentation of the global internet into national networks with divergent user experiences. This phenomenon — sometimes called the “splinternet” — carries economic and social costs that are difficult to reverse once established.
The Operational Cost That ISPs Absorb
Beyond the public policy debate, ISPs in Latam face concrete operational consequences from DNS blocking mandates:
- List maintenance: blocked domains must be continuously updated — new domains, domains that change, domains that reappear under similar names.
- Blocking infrastructure: implementing and maintaining RPZ (Response Policy Zones) or equivalent mechanisms carries a real technical cost.
- Legal risk from over-blocking: if the block affects legitimate content, the ISP may face claims.
- Incompatibility pressure: corporate clients with security policies requiring DoH or DNSSEC may see their services degraded by blocking mandates.
What Internet Society Proposes Instead
The alternatives Internet Society proposes are more operationally demanding but more effective in the long run:
- Act at the source: work with hosting providers and domain registrars to remove illegal content at origin, not just obscure it in the DNS
- Due process: legal action with judicial oversight before implementing blocks, not unilateral administrative lists
- International cooperation: for cross-jurisdictional content, collaboration protocols between authorities that don’t require fragmenting the DNS
The ISP’s Position: Between the Regulator and the Open Network
ISPs in Latam are caught in the tension between regulatory compliance and the technically sound operation of their network. It’s not an easy position.
What is possible — and advisable — is:
- Technically documenting the impacts of mandates before implementing them, as input for regulatory dialogue
- Participating in public policy forums such as working groups at LACNIC, LACNOG, ISOC Latam, and internet policy forums
- Implementing blocks with maximum precision: well-configured RPZ, with periodic list review and appeal processes for erroneous blocks
DNS blocking won’t disappear from the regulatory toolkit. But understanding its limits — and communicating them rigorously to decision-makers — is part of the role that responsible ISPs must play in Latin America’s internet ecosystem.
Is your ISP facing DNS blocking mandates and trying to understand their technical, operational, or regulatory implications? At Ayuda.LA we work with ISPs across Latam on the technical analysis of these measures and on building solid arguments for dialogue with regulators. If you’d like to talk about this issue, reach out.