TCP IP Illustrated

Segment 8 53 bytes is a combination of two telnet

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Unformatted text preview: ent. Segment 3 is line 9 from Figure 26.12, the DO TERMINAL TYPE command. Segment 5 contains the next eight option responses from the server, lines 10-17 from Figure 26.12. file:///D|/Documents%20and%20Settings/bigini/Docum...ti/homenet2run/tcpip/tcp-ip-illustrated/telnet.htm (23 of 26) [12/09/2001 14.47.45] Chapter 26. Telnet and Rlogin: Remote Login The length of this segment is 27 bytes because lines 10-16 are regular options, each requiring 3 bytes, along with the suboption (line 17), which requires 6 bytes. The 12 bytes in segment 6 correspond to line 18, the client sending the suboption with its terminal type. Segment 8 (53 bytes) is a combination of two Telnet commands with 47 bytes of data to be output on the terminal. The first 6 bytes are the two commands from the server: WILL ECHO and DO ECHO (lines 19 and 21). The next 47 bytes are: \r\n\r\nUNIX(r) System V Release 4.0 (svr4)\r\n\r\0\r\n\r\0 The first 4 bytes produce the two blank lines before the string is output. The 2-byte sequence \r\n is considered a newline by Telnet. The 2-byte sequence \r\0 is considered a carriage return. This segment shows that data and commands can appear in the same segment. The Telnet client and Telnet server must scan every byte they receive, looking for the IAC byte and then processing what follows. Segment 9 contains the final two options from the client: lines 20 and 22. The response in segment 10 is line 23, the final option from the server. From this point in the time line user data is exchanged across the connection. There is nothing to prevent additional option negotiation, we just don't see any in this example. Segment 12 is the login: prompt from the server. Segment 14 is the first character we type of our login name, with its echo returned in segment 15. This is the type of interactive traffic we saw in Section 19.2 with Rlogin: one character at a time sent by the client, with the server performing the echo. The option negotiation in Figure 26.12 is initiated by the client, but throughout this text we've been using the Telnet client to conne...
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