What Is DNS — and Why Can One Small Fault Make the Internet Feel Broken?

The Internet Is Not Magic — It Is a Chain of Small Jobs Done Very Quickly

Most students use the internet every day without really thinking about what happens underneath.

You type:

www.google.com

www.hemelprivatetuition.co.uk

and a web page appears.

It feels instant. It feels simple. It feels almost magical.

But behind that simple action is a whole sequence of computing processes:

Your computer must understand the name you typed.
It must find the correct server.
Data must be routed across many networks.
The reply must find its way back.
Your browser must assemble the web page.

At A level, students often learn about DNS, IP addresses, routers, packets, and routing algorithms as separate topics. The problem is that the real internet does not treat them as separate. They work together.

DNS helps your computer find the destination.

Routing algorithms help the data get there.

When DNS fails, your computer may still be connected to the internet, but it can feel as if the whole internet has stopped working.

That is why DNS faults can be so confusing.

What Is DNS?

DNS stands for:

Domain Name System

It is often described as the phone book of the internet, but that description is only partly useful.

A better way to think of DNS is this:

DNS translates human-friendly names into computer-friendly addresses.

Humans like names such as:

bbc.co.uk
google.com
hemelprivatetuition.blogspot.com
pmrsailing.uk

Computers do not use those names directly to send data. They use IP addresses.

An IP address might look like this:

142.250.200.14

or, for IPv6:

2a00:1450:4009:81a::200e

To a human, those numbers are not very memorable. To a computer, they are exactly what is needed.

So when you type a website name, your computer has to ask:

“What IP address belongs to this domain name?”

DNS provides the answer.

A Simple Analogy: Sending a Letter

Imagine you want to visit a friend, but you only know their name.

You know the person is called:

Sarah Jones

That is useful socially, but it is not enough to post a letter or drive to her house.

You need an address.

DNS works in a similar way.

The website name is like the person’s name.

The IP address is like the postal address.

Once your computer knows the IP address, it can begin sending data to the right place.

Why Do We Need DNS?

Without DNS, we would have to remember numerical addresses for every website.

Instead of typing:

www.bbc.co.uk

you might have to type an IP address.

That would be inconvenient, difficult to remember, and unreliable because IP addresses can change.

DNS allows:

websites to have memorable names
companies to move servers without changing their public name
services such as email, websites, cloud storage, and apps to find the correct destination
large organisations to spread traffic across many servers

DNS is not just a convenience. It is a critical part of how the internet works.

What Happens When You Type a Web Address?

Let us follow the journey.

Suppose you type:

www.example.com

Your browser cannot immediately connect to that name. First, it needs an IP address.

Step 1: The Browser Checks Its Own Cache

Your browser may already know the answer because you visited the website recently.

A cache is a temporary store of information.

If the browser has recently looked up the IP address, it can reuse it. This saves time.

Step 2: The Operating System Checks Its Cache

If the browser does not know, the computer’s operating system may have stored the DNS result.

Windows, macOS, Linux, phones, and tablets all keep temporary DNS records.

Step 3: The Computer Asks a DNS Resolver

If the answer is not stored locally, your computer asks a DNS resolver.

This is usually provided by:

your internet service provider
your router
a public DNS service such as Google DNS or Cloudflare DNS
a school, college, or company network

The DNS resolver does the job of finding the answer for you.

Step 4: The Resolver Finds the Correct DNS Record

If the resolver does not already know the answer, it asks other DNS servers.

This may involve:

root DNS servers
top-level domain servers, such as those responsible for .com or .uk
authoritative name servers for the actual domain

Eventually, the resolver gets the IP address and sends it back to your computer.

Step 5: Your Computer Connects to the Server

Now the browser knows where to send the request.

The website name has been translated into an IP address.

Only now can routing properly begin.

DNS Does Not Send the Web Page

This is an important point for A level students.

DNS does not usually deliver the website itself.

DNS simply answers the question:

“What IP address should I use?”

Once your computer has the IP address, other systems take over.

The actual web page is delivered using protocols such as:

TCP
IP
HTTP
HTTPS

DNS is like asking for directions before starting a journey.

Routing is the journey itself.

DNS and Routing: How They Work Together

This is where many students get confused.

DNS and routing are connected, but they are not the same thing.

DNS finds the destination address.

Routing decides how packets travel to that destination.

Once your computer knows the IP address of a server, it must send packets of data across the internet.

These packets may pass through many routers before they reach the final server.

Each router has to decide:

“Where should I send this packet next?”

That decision is made using routing tables and routing algorithms.

What Is a Router Actually Doing?

A router is not just a box in your house with flashing lights.

A router is a device that forwards data packets between networks.

At home, your router connects your local network to your broadband connection.

On the wider internet, much larger routers connect networks belonging to:

internet service providers
universities
data centres
companies
international network providers

Each router looks at the destination IP address in the packet and decides where to send it next.

It does not normally care that the human typed www.google.com.

By the time routing begins, DNS has already translated that name into an IP address.

A Practical Classroom Example

Imagine a student wants to visit:

www.hemelprivatetuition.co.uk

The process is roughly:

The student types the web address into a browser.
The computer asks DNS for the IP address.
DNS returns an IP address.
The browser creates a request for the website.
The request is broken into packets.
The packets are sent to the home router.
The router forwards them to the internet service provider.
Other routers forward the packets across the internet.
The server receives the request.
The server sends packets back.
The browser rebuilds the web page.

This is why the internet is such a remarkable system.

No single router knows the whole internet in detail. Each router only needs enough information to send the packet closer to where it needs to go.

Why Routing Algorithms Matter

A routing algorithm helps decide the best path for data.

The “best” path might depend on:

distance
number of hops
traffic levels
link speed
reliability
network failures
cost

In real networks, routes can change.

If one path becomes unavailable, routers may choose another path.

This is why the internet is resilient. It was designed so that data can often find another way around problems.

However, DNS must work first.

If your computer cannot translate a domain name into an IP address, it may never get far enough for routing to become useful.

The Key Difference Students Must Remember

This is one of the clearest exam-friendly distinctions:

DNS answers: “Where is it?”

Routing answers: “How do I get there?”

DNS provides the IP address.

Routing moves packets towards that IP address.

If DNS fails, the computer may not know where to send the packets.

If routing fails, the computer may know the destination but cannot reach it.

Why DNS Problems Feel So Strange

DNS faults often create misleading symptoms.

You may still be connected to Wi-Fi.

Your router may still be working.

Other devices may still be fine.

Some websites may load.

Others may not.

Email may fail.

SFTP may refuse to connect.

Then, a few minutes later, everything works again.

This can make the fault feel random.

But from a computing point of view, it may be very logical.

The computer is sometimes failing at the name-lookup stage.

It is like saying:

“I can drive, the roads are open, the car has fuel, but I cannot find the address.”

Personal Reflection: When DNS Trouble Looks Like Everything Else

This is not just theory. DNS problems can be incredibly frustrating in real life.

A computer can appear to be connected properly. The Ethernet cable is plugged in. The router is reachable. Other computers on the same switches may work perfectly. The internet may work most of the time.

Then suddenly:

a website will not load
email says the domain cannot be found
an SFTP connection fails
reloading the page makes it work
five minutes later, the same service works normally

That sort of fault is deeply annoying because it does not look like a total network failure.

It looks intermittent.

Intermittent faults are always the most irritating because they disappear just when you try to test them.

For A level students, this is a useful real-world reminder: network problems are not always about whether a cable is plugged in. Sometimes the physical connection is fine, but a higher-level service such as DNS is failing.

Common Symptoms of DNS Failure

A DNS problem may produce messages such as:

“Server not found”
“DNS address could not be found”
“This site can’t be reached”
“Domain not found”
“Name resolution failed”
“Temporary failure in name resolution”

You might also notice:

some websites work while others fail
refreshing the page fixes the problem
apps fail while existing browser tabs still work
email works one moment and fails the next
direct IP connections work but domain names do not

That final one is especially important.

If you can connect to an IP address but not a domain name, DNS becomes a prime suspect.

Why Some Things Still Work During a DNS Fault

This is a subtle point, but it helps explain why DNS faults are confusing.

If your computer already knows the IP address of a website because it recently looked it up, it may have that answer stored in a cache.

So one website might work because the DNS answer is cached.

Another website might fail because the computer needs a fresh DNS lookup.

This creates the impression that the internet is half-working.

In a sense, it is.

The connection may be fine, but the naming system is unreliable.

DNS Caching: Useful but Sometimes Confusing

DNS caching makes the internet faster.

If your computer had to perform a full DNS lookup every single time you loaded a page, everything would be slower.

So DNS records are stored temporarily.

Each record has a TTL, which stands for:

Time To Live

This tells systems how long they should keep the DNS result before asking again.

Caching is useful because it reduces traffic and speeds up browsing.

But it can also cause confusion.

A computer might keep an old DNS answer for a while.

Or a faulty DNS result might persist until the cache is cleared.

That is why one possible troubleshooting step is to clear the DNS cache.

On Windows, this can be done with:


ipconfig /flushdns

This tells Windows to forget its stored DNS results and ask again.

A Practical DNS Troubleshooting Example

Suppose a student says:

“My internet is broken.”

The first question should be:

Is the internet connection broken, or is name resolution broken?

These are not the same.

A structured approach might look like this.

Test 1: Can You Reach the Router?

Try accessing the router’s admin page or pinging the router.

For many home networks, the router might be:


192.168.1.1


192.168.0.1

If the router responds, the local network connection may be working.

Test 2: Can You Reach an External IP Address?

You could test an external IP address.

For example, from a command prompt:


ping 8.8.8.8

If this works, the computer can reach the internet at the IP level.

Test 3: Can You Reach a Domain Name?

Now try:


ping google.com

If the IP address works but the domain name fails, DNS is likely to be the problem.

This is a powerful diagnostic idea:

IP works, name fails = suspect DNS.

What Is Actually Happening During a DNS Fault?

A DNS fault might occur because:

the DNS server is unavailable
the router is not forwarding DNS requests properly
the computer has the wrong DNS settings
IPv6 DNS settings are misconfigured
security software is interfering
a VPN is changing DNS behaviour
a load balancer is sending requests through a faulty line
the DNS cache contains bad information
the network adapter has a driver or configuration problem

Notice that the problem may not be the website.

It may not even be the internet connection.

It may be the system that translates names into addresses.

Why This Matters for Email and SFTP

DNS is not just for websites.

Email also depends heavily on DNS.

When you send an email, systems may need DNS records to find the mail server for the recipient’s domain.

For example, if you email someone at:

example.com

the sending system needs to know which mail server handles email for that domain.

This uses DNS records called MX records.

MX stands for:

Mail Exchange

If DNS fails, the email software may say the domain cannot be found, even though the domain itself is perfectly valid.

SFTP can also be affected.

If you connect to:

ftp.mywebsite.com

sftp.myserver.co.uk

your computer still needs DNS to translate that name into an IP address.

If DNS lookup fails, the SFTP connection may fail before it even tries to log in.

Important DNS Record Types

A level students do not always need huge detail, but it helps to know the main types.

A Record

An A record maps a domain name to an IPv4 address.

Example idea:


example.com → 93.184.216.34

AAAA Record

An AAAA record maps a domain name to an IPv6 address.

IPv6 addresses are longer and written differently.

CNAME Record

A CNAME record points one domain name to another domain name.

For example:


www.example.com → example.com

MX Record

An MX record tells mail systems where to send email for a domain.

TXT Record

TXT records store text information. They are often used for verification and email security systems.

A Simple Way to Picture DNS and Routing Together

Think of ordering a parcel.

DNS is like finding the correct delivery address.

The company name is not enough. The courier needs the address.

Routing is like the parcel travelling through depots and roads.

It may pass through several sorting centres before it arrives.

Packets are like small parcels.

A web page is split into many packets. They may travel through the network and be reassembled at the end.

If the address lookup fails, the parcel cannot even start its journey.

If the route fails, the address is known, but the parcel cannot get there.

Why This Topic Appears in A Level Computing

DNS connects several important A level computing ideas:

networks
protocols
client-server systems
IP addressing
packet switching
routing
caching
reliability
troubleshooting
abstraction

It is also a good example of layered thinking.

Students often want one simple answer:

“The internet is not working.”

But a computer scientist asks:

“Which layer is failing?”

Is it:

the physical cable?
the Wi-Fi connection?
the local network?
the IP configuration?
the DNS lookup?
the route across the internet?
the web server?
the browser?
the application?

This is why computing requires careful thinking rather than guessing.

DNS as an Example of Abstraction

Abstraction means hiding unnecessary detail so that a system is easier to use.

DNS is a brilliant example.

When you type a domain name, you do not need to know:

where the server is physically located
whether the server uses IPv4 or IPv6
whether the website is hosted in one country or many
whether traffic is being balanced between multiple servers
whether the IP address has changed recently

DNS hides much of that complexity.

You use a name.

The system handles the lookup.

This makes the internet usable by ordinary people.

Why the Internet Can Survive Change

Websites move.

Servers are replaced.

Companies change hosting providers.

Cloud services scale up and down.

Without DNS, every user would need to know when the numerical address changed.

With DNS, the domain name can remain the same while the underlying IP address changes.

This is why you can keep using the same website address even when the infrastructure behind it has completely changed.

DNS provides flexibility.

Routing provides movement.

Together, they allow the internet to function at enormous scale.

Practical Example: Changing DNS Server

Sometimes a DNS fault can be investigated by changing the DNS server used by the computer.

Common public DNS services include:


8.8.8.8
8.8.4.4

and


1.1.1.1
1.0.0.1

The first pair is associated with Google Public DNS.

The second pair is associated with Cloudflare.

This does not mean they are always the best choice, but they are useful for testing.

If changing DNS server solves the problem, that suggests the previous DNS resolver may have been unreliable or misconfigured.

However, this should be done carefully, especially on a school, college, or business network, where DNS settings may be controlled for security reasons.

Common Student Misunderstanding: “DNS Is the Internet”

DNS is not the internet.

DNS is one service used by the internet.

The internet is a network of networks using agreed protocols to move data.

DNS is one of the systems that makes it human-friendly.

A useful exam sentence might be:

DNS resolves domain names into IP addresses so that a client can contact the correct server. Routing algorithms then determine how packets are forwarded across networks towards that IP address.

That is a strong A level answer because it links DNS, IP addresses, clients, servers, packets, and routing.

Common Student Misunderstanding: “Routers Use Website Names”

Usually, routers do not route packets based on names such as google.com.

Routers use IP addresses.

By the time packets are being routed, the destination IP address is already inside the packet header.

DNS happens before the connection is made.

Routing happens once packets are being sent.

This distinction is very important.

Common Student Misunderstanding: “If Wi-Fi Is Connected, the Internet Must Work”

Wi-Fi only connects your device to the local network.

You can be connected to Wi-Fi and still have no working internet.

You can have working internet routing and still have broken DNS.

You can have working DNS and still find that a particular website is down.

A connection icon does not prove that every part of the system works.

That is why proper troubleshooting uses tests rather than assumptions.

Mini Revision Summary

DNS

DNS translates domain names into IP addresses.

IP Address

An IP address identifies a device or server on a network.

Router

A router forwards packets between networks.

Routing Algorithm

A routing algorithm helps decide the path packets should take.

Cache

A cache temporarily stores data to make future access faster.

TTL

Time To Live controls how long a DNS result should be stored.

DNS Failure

DNS failure means the computer may not be able to turn a domain name into an IP address.

Exam-Style Question

Question

A student can connect to their home Wi-Fi and can ping an external IP address, but they cannot access websites by typing domain names into a browser.

Explain the most likely cause of the problem.

Model Answer

The most likely cause is a DNS problem. The successful ping to an external IP address shows that the computer has a working network connection and can send packets outside the local network. However, websites typed as domain names require DNS to translate the domain name into an IP address. If DNS is not working, the browser cannot find the IP address of the web server, so the website cannot be loaded using its name.

Another Exam-Style Question

Question

Explain how DNS and routing work together when a user visits a website.

Model Answer

When a user types a domain name into a browser, the computer uses DNS to resolve the domain name into an IP address. Once the IP address has been found, the browser can send a request to the server. The request is split into packets, and routers forward these packets across networks. Routing algorithms help routers decide where to send packets next so that they move towards the destination IP address. DNS identifies the destination, while routing moves the data to that destination.

Practical Activity for Students

Try this on a computer using Command Prompt.

1. Check DNS lookup


nslookup bbc.co.uk

This asks DNS for information about the domain.

2. Ping a domain


ping bbc.co.uk

This tests whether the domain can be resolved and contacted.

3. Ping an IP address


ping 8.8.8.8

This tests whether you can reach an external IP address.

4. Compare the Results

Ask:

Does the IP address respond?
Does the domain name resolve?
Are both failing?
Is only DNS failing?

This is much better than simply saying, “The internet is broken.”

Why This Matters Beyond the Exam

DNS is not just an abstract theory topic.

It affects:

browsing
email
online lessons
file transfers
cloud storage
video streaming
online gaming
website publishing
business systems

For anyone creating websites, uploading files by SFTP, teaching online, sending email, or running a small business, DNS matters.

A fault in DNS can make a perfectly good computer look broken.

It can also make a perfectly good internet connection look unreliable.

That is why understanding DNS is useful well beyond the classroom.

Conclusion: DNS Is Small, Quiet, and Absolutely Essential

DNS is one of those systems that works silently in the background.

Most people only notice it when it fails.

When it works, you type a name and the internet appears.

When it fails, the computer may still be connected, the router may still be flashing happily, and other devices may still work — but websites, email, and file transfers can suddenly become unreliable.

For A level Computing students, DNS is a perfect example of how the internet depends on layers of cooperation.

DNS finds the address.

Routing algorithms help packets travel across networks.

Protocols manage communication.

Servers respond.

Browsers display the result.

The internet feels simple because thousands of complex processes are hidden from the user.

Understanding DNS helps remove some of that mystery.

And once you understand it, the next time someone says, “The internet is broken,” you can ask the much better question:

16 May 2026