A2.2.2 Describe the function of servers · IBDP Computer Science Notes

A server is a computer system, or software running on a computer, that provides data, resources, or services to other computers on a network.
The computers requesting these services are called clients.
Servers are usually designed for:
- high reliability
- fault tolerance
- strong performance

Domain Name System (DNS) server

A DNS server translates a human-readable domain name into its corresponding IP address.
Example:
- www.google.com -> numerical IP address
This process is necessary because network devices route packets using IP addresses, not domain names.

A user enters a domain name into a browser.
The request is sent to the local DNS server.
The local DNS server checks its cache.
If the address is not in the cache, it queries other DNS servers recursively:
- root DNS server
- top-level domain (TLD) server
- authoritative DNS server
The authoritative DNS server returns the correct IP address.
The local DNS server caches the result for a period of time.
The local DNS server sends the IP address back to the client.
The browser uses the IP address to contact the web server.

Why DNS is useful
- makes domain names easier for humans to use
- improves speed through caching
- distributes requests across many DNS servers
- improves reliability through replication and geographical distribution

A DHCP server automatically assigns:
- IP addresses
- subnet masks
- default gateways
- DNS server addresses
This allows devices to join a network without manual configuration.

Discover
- the client sends a broadcast to locate available DHCP servers
Offer
- the DHCP server offers an available IP address
Request
- the client requests the offered IP address
Acknowledgement
- the server confirms the address assignment for a lease period
Why DHCP is useful
- reduces manual configuration
- lowers the chance of configuration errors
- helps ensure each device receives an unique IP address
- supports both dynamic and static-style assignment policies

A file server stores and manages files for users and devices on a network.
It allows multiple users to access shared files such as:
- documents
- images
- videos
- folders
Main functions
- centralized file storage
- controlled file access through permissions
- easier collaboration and sharing
- backup and redundancy support
Reliability and performance
- file servers often use large storage systems
- they may use redundancy such as RAID
- they can support many users accessing files at the same time
Practical applications
- office document sharing
- school shared drives
- centralized storage in organizations

A print server manages printers on a network.
It allows multiple users to send print jobs to shared printers.
Main functions
- queue print jobs
- manage access to printers
- connect many users to one or more printers
- improve efficiency by centralizing printer management
Practical applications
- school computer rooms
- office shared printers
- environments with multiple users and limited printing devices

A mail server handles the sending, receiving, and storage of email.
It may act as:
- a mail transfer agent (MTA)
- a mail delivery agent (MDA)
- or both
Common protocols
- SMTP
  - used for sending email
- POP3
  - used for downloading received email
- IMAP
  - used for synchronizing email across multiple devices
Main functions
- route outgoing email to the correct destination
- store incoming email
- allow users to retrieve messages
- apply spam filtering and security checks
Security features may include:
- spam filters
- antivirus scanning
- sender authentication systems such as:
  - DKIM
  - SPF
  - DMARC

A proxy server acts as an intermediary between a client device and the internet.
Instead of contacting the destination directly, the client sends the request to the proxy server first.
Main functions
- improve security
- improve privacy by hiding the client’s IP address
- filter content and restrict access
- cache frequently accessed resources
- monitor and log requests
Practical applications
- organizations blocking unsafe or inappropriate websites
- schools enforcing internet usage policies
- reducing bandwidth use through caching
- increasing privacy for users

An application server provides the environment and services needed for software applications to run over a network.
It is different from a file server or web server because it focuses on running application logic.
Main functions
- run application code
- process business logic
- connect applications to databases and other services
- support many users accessing the same application
Practical applications
- school management systems
- online booking systems
- enterprise software platforms

Server type	Main function	Example of use
DNS server	Converts domain names into IP addresses	Looking up `www.google.com`
DHCP server	Automatically assigns IP configuration	A phone joining Wi-Fi
File server	Stores and shares files on a network	Shared office documents
Print server	Manages shared printers and print jobs	School printer network
Mail server	Sends, receives, and stores email	Corporate email system
Proxy server	Acts as an intermediary for filtering, privacy, and caching	School web filtering
Application server	Runs networked application logic	School management system
Web server	Hosts and delivers web pages	A company website