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The Illustrated Network- P58

The Illustrated Network- P58: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 21 SMTP and Email 539 Alice Bob MTA Server MTA Server Mailboxes Mailboxes MTA Client Internet MTA Server Email System Email System UA User Agent MTA Message Transfer Agent MAA Message Access Agent FIGURE 21.2 Email over the Internet showing the role of client and server components. bsdserver to bsdclient. It s nice to know that even today complex GUIs and massive directories are not needed to exchange email messages from the command prompt. bsdserver sendmail admin@bsdclient.booklab.englab.juniper.net testing to 10.10.11.177 . bsdserver This email is going to the admin user on bsdclient. The text of the message is testing to 10.10.11.177 and the text entry ends with a single period on a line by itself. Shown in the following is what happens at the receiver starting with the prompt indicating that mail has arrived the period does not appear in the received text . You have new mail. bsdclient mail Mail version 8.1 6 6 93. Type for help. var mail admin 2 messages 1 unread 1 admin@bsdserver.engl Fri Jan 18 22 38 22 1153 U 2 admin@bsdserver.engl Fri Jan 18 22 56 22 1162 2 540 PART IV Application Level Message 2 From admin@bsdserver.booklab.englab.juniper.net Fri Jan 18 22 56 47 2008 Date Fri 18 Jan 2008 22 50 47 -0700 PDT From Administrator admin @bsdserver.booklab.englab.juniper.net To undisclosed-recipients testing to 10.10.11.177 Protocol I Wo 1 0.000000 2 0.000144 3 0.000185 4 0.004319 5 0.004476 6 0.004716 7 0.005205 8 0.007395 9 0.008219 10 0.010505 10.10.12.77 10.10.11.177 10.10.12.77 10.10.11.177 10.10.12.77 10.10.11.177 10.10.12.77 10.10.11.177 10.10.12.77 10.10.11.177 10.10.11.177 10.10.12.77 10.10.11.177 10.10.12.77 10.10.11.177 10.10.12.77 10.10.11.177 10.10.12.77 10.10.11.177 10.10.12.77 TCP ii p TCP SMTP SMTP SMTP SMTP SMTP SNTP SMTP 1710 smtp SYN Seq 0 Ack 0 Win 57344 CHECKSUM INCOF smtp 1710 SYN ACK Seq 0 Ack l Win 57344 CHECKSUM 1710 smtp ACK Seq l Ack l Win 57920 CHECKSUM INCOF Response 220 bsdellent.englab.juniper.net ESMTP Sendm Cccnmand EHLO