Internet and Networking Basics

Internet Basics

• The internet is a wide area network (WAN) comprised of interconnected networks, routers, cables, and satellites.
• The internet is distinct from the World Wide Web, which is a service that operates on the internet.
• Home networks connect to an Internet Service Provider (ISP) through connections like telephone or fibre optic lines.
• ISPs connect to domain name servers (DNS) and internet backbone routers.

The Complexity of Networking

• Networking computers involves many complexities.
• These complexities are managed using protocols to allow devices to communicated.

Protocol Layering

• Protocol layering divides complex networking tasks into smaller, manageable tasks.
• Each layer has a specific responsibility and provides a service to the layer above it.
• Protocol layering reduces complex problems into subproblems.
• This allows devices to be manufactured operating at particular layer.
• This helps different vendors to work together and communicate.

TCP/IP Protocol Stack

• TCP/IP is a crucial protocol stack with four layers that work together.
• Data packets pass through these layers when sent and received.
• The original TCP/IP model had four layers; an updated model has five, splitting the link layer into data link and physical layers.
• The updated 5-layer model accounts for many physical connection options today.
• The four-layer model is sufficient for understanding basic principles.

TCP/IP Layers

• Application Layer: Deals with network applications like web browsers and email.
  • Includes protocols such as HTTP, HTTPS, FTP for web browsing, and SMTP for email.
• Transport Layer: Establishes communication between two hosts.
  • Sets communication settings like language and packet size.
  • Includes TCP and UDP protocols.
• Internet Layer: Addresses packets for transmission and routes them across the network.
  • Uses IP which is the Internet Protocol.
• Link Layer: Manages network hardware, connection port status, and device drivers.
  • Facilitates binary data transmission through various mediums like copper, fibre, and Wi-Fi.

Data Transmission Example

• An example message travels down the TCP/IP stack from the top and is repackaged at each stage before being sent.
• Application Layer: Adds a header with protocols like HTTP, HTTPS, or FTP.
  • The message and header combine to form a segment.
• Transport Layer: Uses TCP and protocols like UDP to establish and maintain connections.
  • Adds port numbers to track sessions to the header.
  • Splits data into packets and adds a sequence number, the total number of packets, and the port number.
• Internet Layer: Adds the source and destination IP address to each packet, forming a socket (IP address + port).
  • Routers operate at this layer and use IP addresses to route packets.
• Link Layer: Adds source and destination MAC addresses to each frame.
  • MAC addresses change at each router hop in a wide area network.

MAC vs. IP Addresses

• Communication on a local area network (LAN) requires the link layer using MAC addresses.
• Communication between different networks requires both the network layer (IP addresses) and the link layer.
• Switches learn and store MAC addresses for connected LAN devices.
• Routers cache some IP addresses.
• MAC address identifies who you are, while IP address identifies where you are.
• Using a MAC Address is like calling someones name in a classroom when you don't know who they are, and having them identify themselves when they respond.
• IP addresses provide a general location for the device.

Data Delivery on Networks

• On the same network, one host can send directly to another, or broadcast to find the destination MAC address.
• The ARP (Address Resolution Protocol) facilitates this process.
• Switches examine MAC addresses to learn which devices are connected to which addresses, reducing the need for broadcasting.
• For different networks, data is transmitted via a router and the destination MAC address will be the address of the router.
• When a frame reaches the router, the router works out where it needs to send the packet by looking at the destination IP and the header.
• The source and destination MAC address are overwritten at each hop on the journey.
• Packets are split up and wrapped with headers and tails, then delivered.
• Final destination will strip off the headers and tails and the application receives the original message.

World Wide Web and DNS

• The World Wide Web consists of hypertext files known as webpages which are hosted on web servers.
• Web servers handles client requests for pages or resources.
• A web page is sent to a web browser, which uses rules to render it correctly.
• A user requests a URL in a browser.
• The browser sends the domain name from the URL to the Domain Name System
• The DNS maps the domain name back to an IP address
• The IP address is then returned to back to the browser
• A get request from the web page is sent to the web server using the IP address
• The requested web page is returned to the client's web browser.

Domain Name System (DNS) Details

• The browser sends the human-readable URL (e.g., www.google.com) to the DNS resolver server.
• The resolver server queries a DNS root name server.
• The root server responds with the address of the top-level domain (TLD) server (e.g., .com).
• The resolver requests the IP address of the domain's name server (google.com) from the .com TLD server, and the .com TLD server responds with the IP address of the domain's name server
• The recursive resolver sends a query to the domain's name server.
• The IP address of google.com is returned to the resolver from its name server.
• The DNS resolver responds to the web browser with the IP address of google.com.
• The DNS involves different domain name servers.
• These domain name servers work together to translate urls into their IP addresses