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IB DP Computer Science Study Notes

C.1.6 Domain and IP Fundamentals

In the realm of IB Computer Science, grasping the intricacies of how the internet operates is pivotal. The bedrock of this understanding is the Domain Name System (DNS) and Internet Protocols (IP) that knit the network of networks into an accessible and functional web.

Domain Name Servers (DNS)

The Role of DNS in the Internet Ecosystem

  • DNS is the cornerstone that allows the use of friendly domain names to navigate the web instead of memorising numerical IP addresses.
  • It acts as a directory service that intelligently translates domain names into IP addresses.

DNS Resolution Process

  • Initial Request: Your browser sends a DNS query when you enter a web address.
  • Recursive Query: The query often passes through several servers, starting from local to more central DNS servers, until the correct IP address is found.
  • Caching: Once found, the IP address is temporarily stored, or cached, to speed up future access.

DNS Record Types

  • A Record: Maps a domain name to its corresponding IPv4 address.
  • AAAA Record: Maps a domain name to its corresponding IPv6 address.
  • CNAME Record: Redirects one domain to another domain.
  • MX Record: Directs email to a mail server.

Internet Protocols

IP (Internet Protocol)

  • Fundamental Tasks: IP is responsible for sending packets of data from source to destination, with each packet independently finding its way.

Structure and Versioning of IP

  • IPv4: The original and most widely used IP version, comprising four-byte (32-bit) addresses.
  • IPv6: A newer version that uses sixteen-byte (128-bit) addresses to accommodate the growing need for more internet addresses.

TCP (Transmission Control Protocol)

  • Reliability: TCP arranges data packets in a specific order and ensures that each packet is delivered error-free.
  • Flow Control: Manages the pace of data transmission to prevent overwhelming the network.

FTP (File Transfer Protocol)

  • File Operations: Beyond file transfer, FTP allows for renaming, deleting, and changing the directories of files on the server.
  • Modes: Includes ASCII mode for text files and Binary mode for binary files like images or programs.

Understanding IP Addresses

IP Address Composition

  • An IP address is composed of two parts: the network part and the host part, which identify the specific network and the specific machine within that network.

Classes of IP Addresses

  • Ranges from Class A to Class E, with A, B, and C being the most commonly used for normal operations of networks.

Dynamic and Static IP Addresses

  • Dynamic IP Addresses: Often assigned by DHCP (Dynamic Host Configuration Protocol) and change with each connection.
  • Static IP Addresses: Permanent and do not change, typically used for servers.

TCP/IP Model Layers

Layer Interaction

  • Each layer in the TCP/IP model interacts with the layer directly above and below it, providing a modular framework for communication.

Protocol Data Units

  • Each layer has its own PDU (Protocol Data Unit), like segments in TCP and packets in IP, that encapsulate data as it moves through the layers.

Detailed Look at FTP

FTP Clients and Servers

  • FTP Clients: Software that initiates a connection to an FTP server to begin file transfers.
  • FTP Servers: Systems that hold the files and manage access and transfers.

Security Concerns with FTP

  • Due to its lack of encryption, FTP's usage has declined in favour of more secure protocols like SFTP (SSH File Transfer Protocol) and FTPS (FTP Secure).

Domain and IP Address Management

Hierarchical Structure of Domain Names

  • Domains follow a hierarchical structure with the top-level domain (TLD) at the highest level, followed by the second-level and subdomains.

Internet Protocol Address Space

  • The IP address space is managed globally to ensure that each address is unique and to facilitate the routing of internet traffic.


  • Subnetting involves dividing a network into smaller networks, allowing for efficient use of IP addresses.

The DNS and IP protocols are the lifeblood of the internet, ensuring that we can find our way in the vast digital expanse and that the data we seek arrives intact and in order. A solid understanding of these systems is essential for students, providing them with the foundational knowledge required for more advanced studies in computer networking and internet technologies.


Supporting both active and passive modes in an FTP client is important due to the variety of network configurations and firewall rules that might exist on client networks. Active mode requires the server to initiate a connection back to the client, which can be blocked by the client's firewall. Passive mode, on the other hand, is initiated solely by the client, which tends to be more firewall-friendly as outbound connections are generally less restricted. By supporting both modes, an FTP client ensures a higher probability of successful file transfer across different network setups.

A domain name is a part of a URL, which stands for Uniform Resource Locator. The domain name represents the address of the hosting server where a website is stored and is a readable version of the IP address. A URL, however, provides detailed information on how to retrieve a resource from its location on the internet. This includes the protocol (e.g., HTTP, HTTPS), the domain name, and often a specific file path to a page or resource on the server. In essence, while the domain name points to where a website is hosted, the URL specifies the exact location of a web page or resource within that website.

Port numbers are an integral part of the transport layer protocols like TCP and UDP. They serve to identify specific processes or services on a host, allowing for multiple services to run simultaneously without conflict. When data arrives at a host, the port number directs it to the correct application or service. For instance, web servers typically listen on port 80 for HTTP traffic and port 443 for HTTPS traffic. Port numbers thus enable a single host to multiplex network service offerings and ensure that data packets reach the appropriate service.

An IP address conflict occurs when two devices on the same network are assigned the same IP address. This results in network issues for the devices involved, typically leading to a loss of network connectivity for one or both devices. To resolve this, network administrators can assign static IP addresses to critical devices to avoid conflicts or configure the DHCP server to ensure it does not duplicate IP addresses. Network protocols such as Address Resolution Protocol (ARP) can also detect and prevent IP conflicts by mapping IP addresses to physical machine (MAC) addresses on the local network segment.

When a DNS server receives a request for a domain not in its cache, it performs a recursive query. The server starts by asking the root name servers for the top-level domain (TLD). The root server responds with a referral to the TLD server, which manages the specific TLD of the requested domain. The TLD server then directs the local server to the authoritative name server for the domain, which holds the actual IP address. The local server caches this response for a certain time, specified by the time-to-live (TTL) value, to reduce the load on upstream servers and speed up future queries.

Practice Questions

Explain the process of DNS resolution when a user attempts to access a website by typing a URL into their browser.

The DNS resolution process begins when a user types a URL into their browser. The browser sends a query to the local DNS server to find the corresponding IP address. If the local DNS server doesn't have the record, it queries higher-level servers. Once the correct IP address is found, it's returned to the browser, which can then initiate a connection to the web server hosting the website. The IP address may be cached to speed up future requests. This process is vital for converting human-readable domain names into machine-readable IP addresses, enabling users to access websites easily.

Discuss the roles of TCP and IP in data transmission over the Internet, and explain how they work together.

TCP and IP play complementary roles in data transmission over the Internet. IP handles the routing of data packets from the source to the destination by attaching destination IP addresses to the packets. TCP ensures reliable delivery of these packets to the correct application at the destination. It establishes a connection, sequences packets for data reconstruction, and checks for errors, requesting retransmission if necessary. Together, TCP/IP ensures that data packets travel across various networks to reach the right destination in the correct sequence and without errors, which is essential for the integrity of data communication on the Internet.

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Written by: Alfie
Cambridge University - BA Maths

A Cambridge alumnus, Alfie is a qualified teacher, and specialises creating educational materials for Computer Science for high school students.

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