An address fails to open. On a phone using a different carrier, the same address opens perfectly normally. Nothing has changed on your device.

That difference isn't coincidence. It comes from how the block was implemented — and understanding it also helps distinguish a genuine block from something merely broken.

Who implements it

Blocking doesn't happen in one central place. What exists is a list issued by the government, which each internet service provider then applies on its own network.

Two direct consequences of that arrangement:

  • Timing differs. One carrier may apply it today, another next week.
  • Methods differ. Some use approaches that are easily bypassed, others use something deeper.

This is what explains why two people in the same city can have different experiences.

Three commonly used methods

1. At the DNS level

The most common and cheapest method. When your device asks for the address of a site name, the carrier's resolver answers with the address of a notice page instead of the real one.

The symptom is distinctive: what appears is a notice page, not an error message. How name resolution works is explained in the guide to what DNS is.

2. By the site name inside the connection

When a device starts an encrypted connection, the name of the destination site is briefly sent in the clear at the start of the exchange. That portion — known as SNI — can be read by equipment along the path, and the connection is cut if the name is on the list.

The symptom differs: the connection fails or drops abruptly, rather than a tidy notice page. This method isn't affected by changing DNS.

3. By IP address

All traffic to a particular address is stopped. This is the least used method for content blocking, because a single IP address often hosts hundreds of sites — blocking it takes unrelated sites down too.

Telling a block from a fault

Before concluding there's a block, these three checks are usually enough:

Try from another network

Turn off Wi-Fi and use mobile data from a different carrier. If it opens there, it's most likely a block on the first network. If both fail, the cause is something else.

Look at the page that appears

An official notice page means DNS-level blocking. An ordinary browser error message more often means the site itself is having trouble, or blocking by the second method.

Test temporarily with another resolver

If the site opens after changing DNS, the block was at DNS level. If it still doesn't open, the filtering is deeper — or the problem isn't a block at all. The steps are in the guide to changing DNS.

A site failing to open often isn't about blocking. A carrier's resolver having trouble produces very similar symptoms, and happens far more often. How to confirm it is in the guide to a DNS server not responding.

The authority to block stems from provisions on electronic information and transactions and their implementing regulations, which give the government grounds to order access to be cut to content deemed unlawful. Common categories include online gambling, pornographic content, copyright infringement, fraud, and content deemed to endanger public order.

Internet service providers are required to carry out those orders on their networks. Site owners who believe they have been blocked in error have a review process available — though in practice it takes time.

For business owners and Wi-Fi providers

Two things are worth knowing if you provide Wi-Fi to others.

First, carrier-level blocks still apply on your network. You don't need to install anything, and you can't switch them off for visitors.

Second, you can add your own filtering on top — blocking certain categories in a café, clinic, or school, for instance. The most practical approach is DNS-level filtering, because it applies to every device at once with nothing to install. Its use in educational settings is covered in the guide to Wi-Fi for schools and tutoring centres.

Liability for what other people do through your network is covered separately in the guide to Wi-Fi owner responsibility.

On the tools used to get around it

This question keeps coming up, and the answer needs splitting in two because the parts get conflated.

The tool itself. VPNs aren't banned, and are routinely used for legitimate purposes — employees connecting to an office network, or someone protecting their traffic on public Wi-Fi. The limits of what they do are covered in the guide to VPNs for public Wi-Fi.

What's accessed. This is the decisive part. Content that is itself unlawful — online gambling, for instance — carries consequences regardless of how it was reached. The tool is legal; the act may not be.

Free VPN services carry their own risk. Running that infrastructure is expensive, and a service charging nothing has to cover it elsewhere — often from its users' data. You're moving trust from your internet provider to a party that's usually far harder to trace.

This article explains how blocking works and where the legal limits sit; it isn't legal advice for a particular situation. For matters affecting your business, consulting a legal adviser remains necessary.

In short

Blocks are implemented by each carrier on its own network, with methods and timing that aren't uniform — which is why results differ between users. Most are implemented at DNS level, where the symptom is a notice page.

And the most frequently forgotten point: a site failing to open is more often caused by something ordinary than by blocking. Check from another network before concluding anything.

Frequently asked questions

Why does a site open on one carrier but not another?

Because blocks are implemented by each internet service provider on their own network, and they don't all apply them at the same time. Differences in the method each carrier uses also make the results uneven.

Does a site failing to open always mean it's blocked?

Not necessarily. The same symptom can come from a malfunctioning DNS resolver, the site itself being down, or a misconfiguration on your device. Telling them apart takes a couple of simple checks before drawing conclusions.

Does changing DNS remove a block?

Only for blocks implemented at the DNS level, and even then not always. Carriers using deeper filtering will still hold the connection back even when the site name resolves successfully.

Is bypassing a block against the law?

Tools like VPNs aren't banned and are routinely used for work. What matters is what you do afterwards — accessing content that is itself unlawful carries consequences regardless of how you reached it.