2. The Context of Cybersecurity: Cyberspace 37 Table 2.7 A minimal Python server and client that recreates the first “Internet” message. We (Internet users) operate at the edge of the network using applications written by programmers. All of the Internet processing and routing takes place in the core of the network and is transparent to us. Unlike programmers, we do not even need to know about IP addresses or port numbers in order to use the Internet. As stated in Section 2.3.4, the main Internet application we use is the web browser. We use web browsers to access the World Wide Web (the Web). Tim Berners-Lee invented the Web in 1989 when he defined the URL (Uniform Resource Locator), HTTP (Hypertext Transfer Protocol), and HTML (Hypertext Markup Language). These three technologies work together to enable web browsing. Hypertext is formatted text that enables linking to URLs. This is a powerful concept and is the reason why it is called “the Web” because links are like spider web strands that tie Internet resources to one another. HTML defines the syntax for web pages and HTTP is the network protocol web browsers and web servers use to communicate. HTTP has evolved considerably since Berners-Lee invented it. Today a secure version is used called HTTPS. When browsing the web, we access resources using URLs. A URL is a unique name for a resource on the world wide web. URLs have a well-defined hierarchical structure: [protocol]://[subdomain].[primary domain].[top level domain]/[resource path] Not all URLs include a forward slash and resource path, and resource paths can include multiple forward slashes and at most one period. Subdomains are optional and there can be multiple sub-subdomains. The most common subdomain is www which stands for world wide web. Figure 2.13 shows a labeled URL. The most important part of the URL is the primary domain—it ties a real-life entity to the resource because domains are leased and publicly registered. The primary domain is the section of the URL immediately before the top level domain (TLD). Some common TLDs are .com, .org, .edu, .net, and .gov, but numerous other TLDs exist. You can always identify the TLD because it comes immediately before the first forward slash if any are present, and if no forward slashes are present, it is the last part of the URL.
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