2. The Context of Cybersecurity: Cyberspace 31 The computing devices on the Internet form a connected graph made up of nodes and links. A connected graph means that there exists at least one path between any two nodes. In this case, the nodes are computing devices. This means it is possible for any two devices on the Internet to communicate with one another—at least in principle. In practice, firewalls and other technologies prevent certain paths. This is similar to the way the roadway system works in the continental United States. Our roadway system forms a connected graph made up of homes and intersections (nodes) and roads (links). A car can get from any home A to any other home B by traveling along a series of roads. Some roads are small and quiet and others are major highways full of traffic. The Internet has an analogous system of network links that carry data across the country and, via undersea cables and satellite links, all over the world. And just like the roadways, links vary in bandwidth. Bandwidth is the amount of data that a link can carry, and is comparable to the number of lanes on a road. Highways have high bandwidth—many cars can travel on them at the same time. The backbone links on the information superhighway (i.e., the Internet) also have high bandwidth and carry huge amounts of data traffic. 2.4.1 The Five Layer Model “We believe in rough consensus and running code.” - Internet Engineering Task Force slogan Many different protocols are involved in computer network communication. A protocol is a specification for communicating over a network. Protocols are like programming languages in that they define keywords and a syntax. They also define actions and the proper order of messages. When two computers “speak” the same protocol, they can communicate information to one another. The Internet protocols are managed by the Internet Engineering Task Force (IETF)—a group of mostly volunteers who since 1986 has aspired to “make the Internet work better.”6 The standards documents used by the IETF are called RFCs (requests for comments). The vast majority of RFCs are serious and professional, but not all. As an example particularly fitting for cybersecurity, RFC 3514 was released April 1, 2003 (yes, April Fools’ Day), and it creates a standard declaring that hackers must set an “Evil Bit” field in their attack traffic so that cyber defenders can more easily recognize malicious traffic and defend against it! Computers communicate by sending signals to one another over links. The communication is coordinated through a layered network architecture.The Internet architecture is a five layer model (see Table 2.6). Each layer handles different aspects of the communication, and neighboring layers pass data up and down to one another. Messages start their journey at the application layer and are passed down through the other layers before being sent onto the network by the physical layer. When the message reaches the destination computer, it is received first by the physical layer, and then it is passed back up to the application layer. 6 ietf.org website. Introduction to the IETF - Mission. Retrieved June 2025.
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