tailieunhanh - The Illustrated Network- P37

The Illustrated Network- P37: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 13 Routing and Peering 329 Loopback Usually called lo0 on Unix-based systems and routers this is the prefix 127 8 in IPv4 and 1 in IPv6. Not only used for testing the loopback is a stable interface on a router or host that should not change even if the interface addresses do. The host itself There will be one entry for every interface on the host with an IP address. This is a 32 address in IPv4 and a 128 address in IPv6. The network Each host address has a network portion that gets its own routing table entry. The default gateway This tells the host which router to use when the network portion of the destination IP address does not match the network portion of the source address. Gateway or Edge Router A lot of texts simply say that the term router is the new term for gateway on the Internet but that this old term still shows up in a number of acronyms such as IGP . Other sources use the term gateway as a kind of synonym for what we ve been calling the customer-edge router meaning a router with only two types of routing decisions that is local or Internet. A DSL router is really just a gateway in this terminology translating between local LAN protocols and service provider protocols. On the other hand a backbone router without customer LANs is definitely a router in any sense of the term. In this book we ll use the terms gateway and router interchangeably keeping in mind that the gateway terminology is still used for the entry or egress point of a particular subnet. Routing Tables and FreeBSD FreeBSD systems keep this fundamental information in the etc default file. But this information can be manipulated with the ifconfig command which we ve used already. However interface information does not automatically jump into the routing table unless the changes are made to the file. If the network_interfaces variable is kept to the default of auto the system finds its network interfaces at boot time. Let s use the netstat -nr command to take a .