WEILAI Online Academic assistant
WEILAI Online Academic assistant
Back to 课程

Computer Science AS OCR

0% Complete
0/0 Steps
  1. 1-1-structure-and-function-of-the-processor as
    5 主题
  2. 1-2-types-of-processor as
    3 主题
  3. 1-3-input-output-and-storage as
    2 主题
  4. 2-1-systems-software as
    8 主题
  5. 2-3-software-development as
    5 主题
  6. 2-4-types-of-programming-language as
    4 主题
  7. 3-1-compression-encryption-and-hashing as
    3 主题
  8. 3-2-databases as
    3 主题
  9. 3-3-networks as
    8 主题
  10. 3-4-web-technologies as
    13 主题
  11. 4-1-data-types as
    8 主题
  12. 4-2-data-structures as
    4 主题
  13. 4-3-boolean-algebra as
    1 主题
  14. 5-1-computing-related-legislation as
    4 主题
  15. 5-2-moral-and-ethical-issues as
    9 主题
  16. 6-1-thinking-abstractly as
    3 主题
  17. 6-2-thinking-ahead as
    1 主题
  18. 6-3-thinking-procedurally as
    3 主题
  19. 6-4-thinking-logically as
    2 主题
  20. 6-5-thinking-concurrently as
    2 主题
  21. 7-1-programming-techniques as
    9 主题
  22. 8-1-standard-algorithms-and-big-o-notation as
    8 主题
课 Progress
0% Complete

Exam code:H046

Domain Name System (DNS)

What is the domain name system?

  • The Domain Name System (DNS for short) can be thought of as the Internet’s equivalent to a phone book

  • It is essentially a directory of domain names and is used to translate human-readable domain names to the numeric IP addresses that computers use

  • When you type a URL into your browser, the DNS translates the domain name into its associated IP address so your computer can connect to the server hosting the website

  • Without DNS, we would have to remember the IP address of every site we want to visit

  • When a domain is newly registered, or a server changes its IP address, the DNS record for that domain needs to be updated in what’s known as DNS propagation

Components of DNS

DNS resolver

  • The first stop in the DNS lookup process, usually provided by your internet service provider (ISP) or a third-party service like Google DNS or OpenDNS

Root servers

  • The resolver asks a DNS root server to find the top-level domain (like .com, .org, .edu)

TLD (Top-Level Domain) servers

  • The root server directs the resolver to a TLD server, which stores the information of the domain

Authoritative DNS servers

  • The TLD server then responds with the IP address of the domain’s authoritative DNS server, which the resolver asks for the IP of the domain

Benefits of DNS

  • DNS allows us to use easily remembered domain names instead of hard-to-remember IP addresses

  • DNS servers handle the mapping between domain names and IP addresses, relieving end users and system administrators from the task

What happens when you type a URL into a web browser?

  1. URL Entry: The user enters the URL of a website into the web browser

  2. The computer checks its local cache to see if it contains the IP address of the URL from a previous request

  3. DNS Query: The web browser sends a query to a DNS server (usually hosted by your ISP) to translate the URL (domain name) into an IP address

  4. DNS Resolver: The DNS resolver checks its cache to see if it has the IP address for the requested domain. If not, it sends the request to the DNS root servers

  5. Root Server Query: The root server directs the resolver to a Top-Level Domain (TLD) server (like .com, .org) based on the extension of the URL

  6. TLD Server Query: The TLD server then provides the resolver with the IP address of the domain’s authoritative DNS server

  7. Authoritative Server Query: The resolver queries the authoritative DNS server for the IP address of the domain

  8. Retrieve IP Address: The authoritative DNS server responds with the IP address for the requested domain

  9. Request the Web Page: The web browser sends an HTTP or HTTPS request to the IP address it received

  10. Server Response: The server at the given IP address processes the request and sends back the data for the web page (HTML, CSS, JavaScript, etc.)

  11. Render the Web Page: The web browser renders the received data into the web page that you see

  • DNS (Domain Name System) translates human-friendly URLs into computer-friendly IP addresses

  • HTTP/HTTPS are protocols defining how messages are formatted and transmitted on the World Wide Web

  • The entire process happens in a matter of milliseconds, making the web user-friendly and efficient

Worked Example

Shreya is a web developer who creates web pages for a variety of different companies.

In order to view a website, a user enters a website address into their web browser such as http://www.ocr.org.uk. The website will then be displayed onto the user’s screen.
Explain how the Domain Name System (DNS) plays a role in websites being loaded.

4 marks

How to answer this question:

  • Since this question is worth 4 marks you need to explain how the DNS system works rather than just state what it does

Answer:

Example answer that would get full marks:

The DNS is a distributed system that finds the IP address of a particular URL. 
The first thing that happens is that the URL is sent to a computer called a DNS resolver. 
This checks its cache to see if it has already looked up this URL. If it hasn’t it will then ask a top-level domain name server (TLD), which again checks its cache to see if it has done this lookup before.
If not it will then continue on and ask the authoritative name server for that domain.

Responses

您的邮箱地址不会被公开。 必填项已用 * 标注