URLs, DNS and DNS Resolution

Unique Resource Locators  (AKA Web Address)

An URL (aka web address) is the alpha-numerical address that humans type in to a web browser to access a website. Humans like to use URLs rather than IP Addresses because they are easy to remember.

An URL can be the name of a website or a specific page and may also contain query parameters / port numbers.

Example URLs

• Website Address – https://www.google.com
• Webpage Address- https://learnlearn.uk/alevelcs/
• Webpage address with search query – https://learnlearn.uk/alevelcs/?s=internet

How Simple HTML Pages are served

When you type in an URL (e.g. www.catgifs.com) into your browser your computer needs to find out the IP address associated with the address in order to send a GET request to the website’s server.

The steps of the process are as follows:

1. The user enters the URL of the website/web-page to be loaded into a web browser. The browser looks in the computer’s DNS cache to see if a matching IP address is stored.
   ** If not found → step 2 / Found → step 4 **
2. A request is sent to the ISP’s DNS resolver server to find out the IP address. The DNS resolver looks for the IP address and if it is stored the DNS Server returns the IP address to the originator.
   ** If not found → step 3 / Found → step 4 **
3. The request is passed on to a higher level DNS. Once found the original DNS caches the IP address for future use and returns the IP address to the user.
4. The browser uses the IP address to send the web page request to the web server.
5. The web server retrieves the page and sends it to the originator.
6. The browser interprets the script and loads the page.

Tutorial Video

Domain Name Service Resolution

The internet works using IP Addresses, so all URLs must be translated(resolved) into and IP address. This is known as DNS resolution and is the job of the DNS Server.

For example www.google.com and 172.217.10.46 both point to the same place

This is the job performed by the Domain Name Service. Domain name services are usually hosted on servers.

How web pages are served presentation