How Websites Actually Get Blocked: Technical Methods Explained

Imagine you want to visit a news website, but when you type the address into your browser, nothing loads. Was the site taken down? Is your internet broken? Or did someone in between intercept your request and prevent it from reaching its destination?

Website blocking happens constantly around the world—sometimes by governments enforcing censorship, sometimes by network administrators blocking malware, sometimes by internet service providers enforcing copyright rules. The technical methods used to block access vary wildly in sophistication, cost, and effectiveness. Understanding how each one works will help you grasp not only how censorship functions, but also why it's so difficult to implement perfectly and why no single blocking method has completely won out over the others.

DNS Filtering: The Phone Book Approach

When you type a website address (called a domain name) into your browser—say, example.com—your device doesn't automatically know where that site lives on the internet. Instead, it asks a special server called a DNS resolver to look up the address in a giant distributed phone book. The resolver says something like: "example.com? That's at IP address 203.0.113.42." Your browser then connects to that IP address.

DNS filtering works by intercepting that lookup. An authority (government, ISP, or network admin) intercepts DNS requests and returns a fake answer—or no answer at all. When you ask for example.com, instead of getting the real IP address, you get redirected to a blocking page, or your request simply times out.

From a censor's perspective, DNS filtering is cheap and easy. It requires minimal infrastructure—just a few servers sitting between users and legitimate DNS resolvers. It doesn't require inspecting encrypted traffic or upgrading network hardware. It's why many countries start here.

But DNS filtering has a major weakness: it's trivial to bypass. A user can simply ask a different DNS resolver for the answer—one not controlled by the censor. Public DNS resolvers operated by major tech companies or volunteer-run services exist worldwide. This is why DNS filtering alone rarely stops determined users, though it does stop casual browsing.

IP Blocking: Shutting Off a Building

If DNS filtering is like misdirecting a phone call, IP blocking is like physically preventing mail from reaching a building's address. Here, a network authority identifies the IP address (the internet address) of a website server and instructs routers to drop or reject any traffic heading to that address.

IP blocking requires more infrastructure than DNS filtering. Routers must examine every packet of data flowing through them, check its destination IP, and decide whether to allow it. On a massive scale, this demands significant computational power and careful network configuration.

IP blocking also has a critical weakness: many websites share the same IP address. A censor blocking one site may accidentally block dozens of legitimate sites hosted on the same server. This collateral damage is why IP blocking tends to be used selectively, against high-value targets rather than broadly.

Circumventing IP blocking is harder than circumventing DNS filtering, but still possible. A user can route their traffic through another server in a different location—one whose own traffic isn't blocked. This is where VPN services and proxy servers become relevant, though we'll explore that in separate articles.

Deep Packet Inspection: Reading the Envelope

DNS and IP blocking work at crude levels of the network stack. Deep Packet Inspection (DPI) works at a finer grain. Imagine postal mail: DNS and IP blocking are like blocking mail to a certain address. DPI is like opening each envelope and reading the contents to decide whether to deliver it.

DPI systems examine the actual data traveling across a network connection, looking for patterns that indicate a forbidden website, keyword, or activity. If you're trying to access example.com, DPI can identify this from the content of your encrypted request—even without decrypting it—by analyzing the Server Name Indication (SNI) field, which is like a shipping label on the outside of the encrypted envelope. SNI tells the destination server which website you're trying to reach, and it's sent before encryption begins.

DPI is far more expensive than DNS or IP blocking. It requires deploying specialized hardware at multiple points in the network and continuously updating detection patterns. It also creates latency (slowness) as packets are inspected in real time.

Because SNI is sent unencrypted, DPI can block based on it relatively efficiently. But newer protocols like HTTPS with Encrypted Client Hello are beginning to encrypt even the SNI field, making this approach less viable. This is an ongoing technical arms race.

BGP Hijacking and Network-Level Shutdowns

At the most extreme end, censors can intervene at the routing level itself. The Border Gateway Protocol (BGP) is the system that tells routers how to find paths to different networks. A government can theoretically announce false BGP routes, claiming that traffic to a blocked website should be redirected through their own censoring infrastructure.

BGP hijacking is rare and dangerous—mistakes can break internet routing for entire regions. It requires deep control of national internet infrastructure and affects many services at once, often causing widespread outages. Only the most authoritarian governments with tightly controlled internet architecture attempt this.

Throttling and Gradual Degradation

Some authorities don't block access entirely; they make it so slow that the site becomes unusable. This throttling is subtle—technically the site is still accessible, but the artificial delay makes it impractical. It requires DPI-like infrastructure but achieves a "softer" form of censorship that may draw less attention or criticism.

Comparison Across Regions

Countries typically use multiple methods in layers. China employs DNS filtering, IP blocking, DPI (including SNI inspection), and periodic BGP-level interventions. Russia uses DPI and IP blocking at scale. Iran uses DNS, IP blocking, and DPI. Many Western countries use DNS filtering and IP blocking for specific purposes (malware distribution, copyright infringement, child exploitation material), though not for political censorship.

No single method is perfect from a censor's perspective—each has costs, limitations, and workarounds. This is why understanding the technical landscape matters: it shows that censorship is always a cat-and-mouse game, never a completed fortress.

Key Takeaway

Website blocking ranges from simple (DNS filtering) to complex (BGP hijacking), but every method operates at a specific layer of the network and has corresponding weaknesses. Understanding these technical differences helps explain why some countries block more effectively than others, and why circumvention methods target specific layers of the stack. To deepen your knowledge, explore how encrypted DNS, VPNs, and proxy servers work at a technical level—each targets different blocking methods in different ways.