The Illustrated Network- P17:In this chapter, you will learn about the protocol stack used on the global public Internet and how these protocols have been evolving in today’s world. We’ll review some key basic defi nitions and see the network used to illustrate all of the examples in this book, as well as the packet content, the role that hosts and routers play on the network, and how graphic user and command line interfaces (GUI and CLI, respectively) both are used to interact with devices. | CHAPTER 4 IPv4 and IPv6 Addressing 129 Table Use of Default or Natural Subnet Masks Original Class Default Mask Network Host Bits Example Interpretation A 8 24 8 prefix is host on network B 16 16 16 prefix is host on network C 24 8 24 prefix is host on network The more bits the more network identifiers the fewer bits the fewer host identifiers possible. CIDR notation are the most common. Sometimes the default mask for an IP address class is called the natural mask for that type of address. In all cases it is possible to change the default mask to move the boundary between the network and host portions of the IP address to wherever the device needs to see it. All devices whether hosts or routers which need to route the packets within the subnetted network must have identical masks. All routing protocols in wide use today exchange subnet mask information together with routing information. The use of the default masks for the original classful IP address space is shown in Table . The more bits the more network identifiers and the fewer bits the fewer host identifiers possible. Subnetting moves the boundary between the network and host for a particular classful IP address to the right of the position where the boundary is normally found. We will see later that supernetting moves the boundary between network and host for a particular classful IP address to the left of this position. CIDR which uses VLSM can move the boundary anywhere. It is important to realize that subnetting does not change anything with respect to the outside world. Internet routers still deliver the packets as before. It is the customer or site router that applies the subnet mask and delivers packets to the subnets. Instead of the usual two parts of the IP address network and host we now have network subnet and host. However even at the beginning of the .
