Names and DNS

Every site on the internet also has a numeric address, a bit like a phone number for computers. People would find long numbers hard to remember, so we use names such as bbc.co.uk or wikipedia.org.

Your device cannot mail a letter using only a nickname. It needs the real address. DNS, which stands for Domain Name System, is the service that looks up a name and returns the number.

Open the DNS lab beside this lesson. Pick a preset or type a name, then step through the lookup. Watch the question travel to a DNS server and the number come back.

When you open a site, your device often asks a DNS server at your school or home first. If that server knows the answer, it replies quickly. If not, it asks another DNS server up the chain.

The answer is cached, which means stored for a short time. That way the same name does not need a full lookup every second. Cached answers make the web feel fast.

If you spell a name wrong, DNS cannot find a match. Your browser may show an error page instead of the site you wanted.

DNS is powerful because it decides which number belongs to a name. Tricksters sometimes try fake lookups to send you to the wrong site. That is one reason HTTPS and careful clicking matter later.

Official school sites use names you recognise. If a link swaps one letter, the name looks similar but the lookup may point somewhere else entirely.

Next you will follow packets, the small chunks of data that carry requests and answers across the internet.