Cambridge O Level Computer Science · Syllabus 2210 · The Internet and its Uses
Domain Name Server
What is Domain Name Server?
A domain name server (DNS) holds records that match domain names to IP addresses; when a browser supplies a domain name the DNS returns the corresponding IP address, or passes the query to another DNS server, so that a request can be sent to the correct web server.
This definition is part of the The Internet and its Uses chapter in Cambridge O Level Computer Science.
Domain Name Server in context
The internet is the worldwide infrastructure of interconnected networks. The world wide web is the collection of websites and web pages that is accessed using that infrastructure. When you type a URL, the browser separates out the domain name, asks the domain name server (DNS) to turn it into an IP address, sends an HTTP or HTTPS request to the web server at that address, receives HTML and other resources back, and renders the page on your screen. Along the way the browser may store cookies. The same infrastructure carries digital currency transactions, which a blockchain records as time-stamped, hash-linked blocks so that a change to an old record is detectable. And because everything above is reachable from anywhere, Topic 5 finishes with the cyber security threats that exploit it and the layered solutions that reduce them.
When a user enters a URL, the browser separates out the domain name and asks the domain name server (DNS) to translate it into the web server's IP address. Once it has that address the browser sends an HTTP or HTTPS request to the web server, which processes the request and returns a response containing the HTML and the other resources the page needs. The browser then renders that HTML and displays the finished page. DNS supplies an address; the web server supplies the page; the browser draws it.
Common mistakes with Domain Name Server
- M2 — "A URL is an IP address." Why it is wrong A URL is a text-based address containing a protocol, a domain name and often a path and file name. An IP address is a numerical address identifying a device. They are connected only because DNS converts the domain name inside the URL into an IP address. Say instead "The URL contains a domain name, which the domain name server resolves to the web server's IP address."
- M4 — "The DNS sends the web page back to the browser." Why it is wrong The domain name server returns an IP address and nothing else. The web server stores and returns the page. Say instead "The DNS returns the IP address; the browser then sends its request to the web server, which returns the HTML."
Examiner tips on Domain Name Server
- The three sentences most worth memorising word for word, because each one closes off a whole family of errors: "The world wide web is the collection of websites and web pages accessed using the internet." "The domain name server returns the IP address; the web server returns the page; the browser renders it." "Each measure reduces particular risks and leaves others open, so several complementary layers are used together."
Questions students ask about Domain Name Server
How does a browser turn a typed URL into a displayed web page?
The browser separates the domain name out of the URL and asks the domain name server (DNS) to translate it into the web server's IP address. Once it has that address, the browser sends an HTTP or HTTPS request to the web server, which returns the HTML and other resources the page needs. The browser then renders that HTML and displays the finished page. DNS supplies an address, the web server supplies the page, and the browser draws it.