Another round of site-blocking legislation is moving through Congress, this time targeting DNS infrastructure as the enforcement mechanism. The technical and operational implications for ISPs, DNS operators, and hosting providers merit closer examination than the policy headlines typically allow.
The DNS Blocking Approach
Rather than focusing solely on ISP-level blocking, the latest proposals—including a bill from Rep. Darrell Issa—extend requirements to DNS resolvers themselves. This represents a shift in targeting infrastructure, moving enforcement upstream from the border gateway level to the recursive resolver that billions of queries pass through daily.
In technical terms, the mechanism is straightforward: when a user's device queries a resolver for a domain associated with copyright infringement, that resolver would be obligated to return a blocked response rather than the legitimate IP address. The challenge lies in the definition, enforcement, and operational burden this creates across an already complex DNS ecosystem.
Operational Challenges for Resolver Operators
Public DNS resolvers—whether operated by ISPs, tech companies, or independent services—already maintain filtering lists for malware, phishing, and in some regions, political censorship. Adding mandatory copyright enforcement to this mix introduces several complications.
First, there is no single authoritative list of infringing domains. Copyright holders, enforcement agencies, and private platforms all maintain different lists with varying accuracy and update frequency. A resolver operator would need to reconcile multiple sources, handle disputes over listings, and manage the liability exposure when legitimate domains are blocked by mistake.
Second, the operational overhead is non-trivial. Resolver infrastructure must handle millions of queries per second with microsecond latency. Implementing real-time list lookups against growing block lists introduces latency, increases CPU and memory footprint, and creates new failure modes. A resolver that goes offline due to overload becomes a DNS amplification attack vector.
Third, technical workarounds are well-established. DNS-over-HTTPS (DoH) and DNS-over-TLS (DoT) encrypt queries so that network-level filtering cannot see which domain is being resolved. Users can switch to resolvers in other jurisdictions, including those specifically designed to ignore blocking mandates. These are not hypothetical—they are already widely deployed.
The Jurisdictional Complication
A DNS resolver operator is not always a U.S. entity. Services like Cloudflare's 1.1.1.1, Quad9, and others operate globally and must comply with local laws in each jurisdiction where they have users or infrastructure. A U.S. mandate to block copyright domains could conflict with rules in Europe, Asia, or other regions where such blocking is prohibited or where different domains are considered infringing.
For hosting providers operating in multiple jurisdictions—particularly those offering services from offshore datacenters—this creates practical compliance nightmares. An operator managing DNS infrastructure across multiple countries cannot unilaterally block a domain without potentially violating the laws of another nation.
Where This Leaves the Industry
Legislation often assumes technology works the way policymakers imagine rather than how it actually does. DNS blocking bills are not new; similar proposals have circled Congress before, typically without passage. The opposition this time includes both privacy advocates concerned about mandatory filtering and technical operators concerned about feasibility and liability.
For infrastructure operators, the most prudent approach is to monitor legislative progress closely and document the technical constraints. When enforcement discussions begin, providing genuine technical input—not lobbying hyperbole—can shape more workable requirements. Blocking at the DNS level is not impossible, but the costs, workarounds, and jurisdictional conflicts deserve explicit acknowledgment in law before it passes.
