tailieunhanh - The Illustrated Network- P54

The Illustrated Network- P54: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 499 FIGURE DNS records on winsrv1 using a GUI. Note the various record types the name servers in particular . lnxserver Server Address 53 Non-authoritative answer Name Address Simple DNS has a nice GUI in contrast to the text files used in most Unix DNS versions as shown in Figure . The Ethereal capture in Figure shows the utter simplicity of the DNS message exchanges. There s even a nice log of these messages as shown in Figure it also tracks DHCP leases when dynamic DNS is used . Now we can finally ping on the Illustrated Network the normal way. root@lnxclient admin ping PING 56 84 bytes of data. 64 bytes from icmp_seq 1 ttl 126 time ms 64 bytes from icmp_seq 2 ttl 126 time ms 500 PART IV Application Level FIGURE DNS server reply. Note that the question field shows up as queries. FIGURE DNS server log showing the history of queries and responses. CHAPTER 19 The Domain Name System 501 64 bytes from icmp_seq 3 ttl 126 time ms 64 bytes from icmp_seq 4 ttl 126 time ms 64 bytes from icmp_seq 5 ttl 126 time ms 64 bytes from icmp_seq 6 ttl 126 time ms 64 bytes from icmp_seq 7 ttl 126 time ms AC ping statistics 7 packets transmitted 7 received 0 packet loss time 8080ms rtt min avg max mdev ms root@lnxclient admin LAN1 is also running a DNS server on lnxserver and to keep the configuration very simple only functions as a non-authoritative server. The configuration is