tailieunhanh - The Illustrated Network- P53

The Illustrated Network- P53: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 19 The Domain Name System 489 Root Server Details Table shows the 13 root name servers A through M who operates them their locations and their IP addresses IPv4 and IPv6 where applicable . For the latest information which changes from time to time for example the IPv4 address of changed in 2004 see . Note that many of the root servers although all grouped under a single name are actually many systems spread throughout the world. This is where anycast is useful. In the past the willingness of DNS servers to accept updates from any source when offered was a major security weakness. Modern DNS servers accept only authorized and digitally signed updates and higher level DNS servers never accept dynamic updates from anyone. One interesting initiative is the continuing development of DNS Security DNSSec . DNS is still a tempting target on the Internet and although DNSSec raises the bar the target remains attractive. DNS IN THEORY NAME SERVER DATABASE AND RESOLVER DNS consists of three essential components the name server the database of DNS resource records and the resolver. An application interacts with name servers through a resolver. This is an application program that resides on user workstations and sends requests for DNS information when necessary. Resolvers must be able to find at least one name server usually the local name server and local DNS servers provide authoritative answers for local systems. The resolver must also be able to use the information returned by the local name server if the resource records needed are not local or cached to pursue the query using referral information leading to other DNS name servers on the Internet. The resource records of the Domain Name Space are grouped and formatted with a strict tree-structured name space. Information is associated with each type of resource record. The sets of local information the zones in this structure are distributed among all DNS servers. The name