What DNS Is and Why It Causes "The Internet Works but Websites Won't Open" — How It Works, When to Change Your DNS Server and Why Hijacking Is Dangerous

Here's a strange situation: messengers on your phone receive messages, but the browser says "Can't reach this site" or "DNS server not responding". Or sites do open, but with a delay of several seconds before each one. In many such cases DNS is to blame — a system the internet as we know it can't work without, although few people have heard of it. Let's look at what DNS is in simple terms, why it fails, when it's worth changing your DNS server and why DNS hijacking is dangerous.

DNS in simple terms

Computers on the internet find each other by numerical IP addresses. People, though, find names easier — such as a website address. DNS is the internet's "phone book": when you type in a website address, your device asks a DNS server what IP address that name has, and only then connects to the site. Normally the DNS server is assigned automatically by your provider, via the router. Answers are remembered for a while, so repeat visits to the same sites happen faster.

Signs of DNS problems

• Websites won't open, while apps that use direct addresses do work.
• Errors such as "DNS server not responding", "DNS_PROBE_FINISHED_NXDOMAIN" or "Server IP address could not be found".
• Sites open with a noticeable delay before they start loading.
• Some sites open and others don't, while friends on a different provider can open them.
• Sites open at their old address after moving to new hosting — an outdated cached record.

Why DNS breaks

• The provider's DNS servers fail — temporary overload or an outage at the provider.
• A frozen router — many routers act as a DNS intermediary themselves and start misbehaving over time.
• Wrong settings on the computer — a manually entered DNS server that doesn't exist, leftovers from a VPN or "internet booster".
• A corrupted DNS cache on the computer or in the browser.
• Malware and a hacked router replacing the DNS servers.
• An antivirus or firewall blocking DNS requests.

When to change your DNS server

Instead of your provider's DNS you can use public DNS servers run by large companies. This can help if your provider's DNS is slow or unreliable, if some sites won't open because of errors in the provider's DNS, or if you want extra protection. Many public DNS services support encrypted queries (DNS over HTTPS or over TLS), which stops others on the network seeing which sites you open. It's most convenient to change DNS on the router — then the setting applies to every device in the house.

DNS filtering

Some DNS servers can block malicious and phishing sites, and family versions block adult sites too. It's a simple way to add protection for the whole family, including children's tablets and TVs, without installing software on every device. In an office, DNS filtering reduces the risk of an employee accidentally opening a fake bank site or an infected page. It's no substitute for antivirus software, but it's a useful extra layer.

DNS hijacking — a dangerous hack

If an attacker gains access to your router — for example through the factory admin password or a vulnerability in old firmware — they can replace the DNS servers. Then when you type in the address of your bank or email, you land on a fake site that looks like the real one. The signs: unfamiliar DNS servers in the router or computer settings, strange certificate warnings, familiar sites looking slightly different, or the browser showing ads where there were none before. In that case you need to reset the router, update the firmware, change all your passwords and check your computers for viruses.

What you can try yourself

• Restart the router and the computer.
• Check whether sites open on another device on the same network, and over mobile data.
• Turn off any VPN or "boosters" you have installed.
• See whether unfamiliar DNS servers have been entered manually in the network adapter settings.

What our technician does

1. Diagnoses the cause: the provider's DNS, the router, the computer, viruses or settings.
2. Checks the router for signs of hacking and DNS hijacking, updates the firmware and changes passwords.
3. Sets up reliable DNS servers on the router, encrypted if needed.
4. Sets up DNS filtering to protect children or staff.
5. Cleans computers of malware and the remnants of network "optimisers".

A real example

The owner of a small shop in Nadzaladevi noticed that when he logged into online banking, the page looked slightly different and asked for the SMS code twice. Our technician checked the router: the admin password was the factory default, the firmware was seven years old, and someone else's DNS servers had been set, redirecting to fake pages. Fortunately the owner had grown suspicious in time and didn't enter the second code. We reset and updated the router, set strong passwords and safe DNS servers with malicious-site filtering, checked the computers for viruses and advised him to change his banking and email passwords.

Call a technician

If you have internet but websites won't open, or you suspect DNS hijacking, we'll come to any district of Tbilisi around the clock. Learn more on our internet not working, router setup and virus removal pages.