The phone book of the internet
People remember names. Computers route traffic using numeric addresses. The Domain Name System, or DNS, is the service that connects the two. When you type a website name, your device first asks a DNS server what numeric address belongs to it, then connects to that address.
This happens constantly and invisibly. A single web page often involves lookups for several names, since it may load images, scripts and adverts from different places. Most of the time the whole process takes a fraction of a second.
How a lookup works
The path of a lookup in general terms is as follows:
- Your device checks its own memory of recent answers (its cache). If the answer is there and still valid, it is used straight away.
- If not, your device asks a resolver, also called a DNS server. At home this is usually your router, which passes the question to a resolver run by your internet provider unless you have chosen another.
- The resolver checks its own cache. Popular names are often already stored.
- If it does not know, it works through the system of name servers: first those that handle the top of the naming tree, then those for the ending of the name such as “.com”, and finally the server responsible for the particular domain, which gives the authoritative answer.
- The answer returns to your device, and each stage may keep a copy for a limited time, set by the domain’s owner.
Because answers are cached, repeat visits are quick, and a change to a site’s address can take a while to spread to everyone.
Why people change their DNS servers
By default, your devices usually use whatever resolver your provider supplies. Some people choose a different one, offered by a third-party company or a non-profit, for several reasons:
- Reliability. If the provider’s resolver is slow or has outages, another may be steadier. Pages can fail to load with an error about the address not being found, even though the connection itself works.
- Speed of lookups. Differences are often small and vary by location and the resolver’s caching. A faster resolver may shave a little off the first load of a site, but it does not make downloads or streaming faster.
- Filtering features. Some resolvers optionally block known harmful sites, or adult content, which some families use as one layer among others. This is not complete protection, and it is not a replacement for parental controls on the devices themselves.
- Privacy preferences. Whoever runs the resolver can see which names you look up. Some people prefer a resolver whose published policy suits them better than their provider’s. The policy still has to be trusted, since you cannot verify it yourself.
- Encrypted lookups. Traditional DNS questions are sent unencrypted, so anyone along the path can read them. Newer methods such as DNS over HTTPS and DNS over TLS encrypt the question between your device and the resolver.
What changing DNS does not do
It helps to be clear about the limits, as DNS is sometimes treated as a magic setting.
- It does not hide your activity from everyone. Your provider can still see which numeric addresses you connect to, which often reveals the service even if the name lookup is private. And the sites you visit still see your address.
- It does not replace a virtual private network. A VPN encrypts and reroutes all your traffic, which is a different thing, and has its own limits. Changing DNS only affects name lookups.
- It does not guarantee safety. Blocking lists catch only known bad sites. Phishing scams and lookalike domains that are new or unlisted may still resolve normally.
- It does not raise your plan’s speed. Download and upload capacity come from the line, and the difference between bandwidth and latency is a separate matter.
- It does not bypass every restriction. Blocks applied by other means will remain.
DNS can also be tampered with by attackers. If a router has been taken over, one trick is to change its DNS setting so that you are sent to fake copies of real sites. This is one reason to set a strong admin password and keep router firmware up to date, and to check from time to time that the DNS setting is what you expect.
Where you can change it
DNS can be set in two places, and the difference matters:
- On the router. The change then applies to every device that gets its settings from the router, which is convenient for a whole household. Some routers hide this setting or let the provider override it.
- On a single device. Phones, computers and some browsers let you pick a resolver for that device alone. Settings in a browser or app may override the device setting.
Before changing, note the existing values so you can restore them, because mistakes can leave you unable to load sites. If something breaks, switching back to automatic settings usually restores normal behaviour. A restart of the device or router afterwards can help apply the change.
Troubleshooting with DNS in mind
DNS is a useful thing to consider when:
- some sites will not load while others do, and you can still reach a site by its numeric address;
- error messages mention the server’s address not being found;
- everything works for a short while after a restart and then fails again.
In these cases, trying another resolver for a short test is a reasonable step. If it makes no difference, the problem lies elsewhere, such as with the line or Wi-Fi.
A sensible takeaway
Changing DNS is a small, reversible tweak that can occasionally improve reliability or add optional filtering. It is not a privacy shield and not a speed upgrade. Treat it as one setting among many, and choose any provider based on its published policies, not on marketing claims.