Networking

Describe the internet in terms of a worldwide communications infrastructure

The largest public network in the world is called the Internet.

The Internet is a network of inter-connected networks.

The World Wide Web is a collection of resources on the Internet.

Structure of the Internet

The main part of the Internet is the backbone.

It is a set of dedicated connections that connect several large networks at various points on the globe.

Each of these points is usually connected to other regional networks controlled by ISPs (internet service providers).

ISPs provide access to end-users.

IP addresses

Each device on a network needs to be uniquely identified, like how a home needs an address. The Internet Protocol addressing system is used.

IPv4 (IP Version 4) addresses consist of four octet values (groups of eight bits) separated by full stops. For example: 140.0.255.10.

Four bytes only allows for 2^(32 bits) = roughly 4.3 billion addresses, which is too small.

This led to IPv6 being invented, consisting of eight groups of 16 bits separated by colons, boasting 2^128 = roughly 340 trillion trillion trillion IP addresses.

Fully qualified domain names

An example is www.bbc.co.uk.

An FQDN can be split into two parts: the host (e.g. www.) and the domain name (bbc.co.uk).

Uniform Resource Locators

URLs are used to specify where a resource across a network should be accessed from.

The protocol and domain name together form the URL.

Example:

- https:// is the protocol (i.e. the website uses HTTPS).

- www.bbc.co.uk/index.html is the FQDN plus the resource to be accessed.

Domain Name System

DNS servers are dedicated computers with an index of domain names and their corresponding IP addresses.

Typing google.co.uk into a browser causes it to first make a DNS request to a DNS server to get an IP address, which is then used to access the website.

Several DNS servers work together to catalogue every web domain name. They are categorised into geographical groupings/levels. When a given domain's IP address is unknown, a query is referred to a bigger domain server that could know.

In this example, a domain name is being revolved into an IP address right to left. We will use youtube.com as an example.

1. A request is sent to the local ISP's DNS server.
2. It doesn't know, so a request is sent to a root DNS server, the highest in the hierarchy.
3. The root DNS provides the local one a reference to a TLD (top-level domain) server, which is .com in this example.
4. The TLD server provides a reference to an authoritative nameserver.
5. The authoritative nameserver provides the IP address of youtube.com to the local ISP's DNS.
6. The local ISP's DNS the IP address of youtube.com to the end-user.
7. The local DNS and the user's personal computer will cache the IP address, so this process doesn't need to be repeated every time one wants to access youtube.com.

Internet Registries

The IANA (Internet Assigned Numbers Authority) is responsible for global IP addresses and domain names.

They allocate IP addresses to five worldwide Internet registries.

These Internet registries delegate domain name registration to many domain registrars. You can purchase domain names from these domain registrars.

Domain names must be unique. Abcde.com and abcde.co.uk are both allowed at the same time, as they are technically still unique.