TCP IP Illustrated


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Unformatted text preview: corresponds to, so the port numbers must be in the first 8 bytes of the TCP header. 17.5 There are options at the end of the TCP header, but there are no options in the UDP header. Chapter 18 18.1 The ISN is a 32-bit counter that wraps around from 4,294,912,000 to 8,704 approximately 9.5 hours after the system was bootstrapped. After approximately another 9.5 hours it will wrap around to 17,408, then 26,112 after another 9.5 hours, and so on. Since the ISN starts at 1 when the system is bootstrapped, and since the lowest order digit cycles through 4, 8, 2, 6, and 0, the ISN should always be an odd number. 18.2 In the first case we used our sock program, and by default it transmits the Unix newline character as itself-the single ASCII character 012 (octal). In the second case we used the Telnet client and it converts the Unix newline into two ASCII characters-a carriage return (octal 015) followed by a linefeed (octal 012). file:///D|/Documents%20and%20Settings/bigini/Doc...omenet2run/tcpip/tcp-ip-illustrated/append_d.htm (11 of 20) [12/09/2001 14.48.04] Appendix D: Solutions to Selected Exercises 18.3 On a half-closed connection one end has sent a FIN and is waiting for either data or a FIN from the other end. A half-open connection is when one end crashes, unbeknown to the other end. 18.4 The 2MSL wait state is only entered for a connection that has gone through the ESTABLISHED state. 18.5 First, the daytime server does the active close of the TCP connection after writing the time and date to the client. This is indicated by the message printed by our sock program: "connection closed by peer." The client's end of the connection goes through the passive close states. This puts the socket pair in the TIME_WAIT state on the server, not the client. Next, as shown in Section 18.6, most Berkeley-derived implementations allow a new connection request to arrive for a socket pair currently in the TIME_WAIT state, which is exactly what's happening here. 18.6 A reset is sent in response to the FIN, because the...
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