TCP IP Illustrated

This option starts with a do since the go ahead

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Unformatted text preview: 4) RCVD DONT ECHO login: rstevens Password: 23. we type our login name and password, which the server does not echo operating system greeting is then output ... then shell prompt Figure 26.12 Initial option negotiation by Telnet client and server. file:///D|/Documents%20and%20Settings/bigini/Docum...ti/homenet2run/tcpip/tcp-ip-illustrated/telnet.htm (20 of 26) [12/09/2001 14.47.45] Chapter 26. Telnet and Rlogin: Remote Login We've numbered the option negotiation lines that begin with SENT or RCVD, for the discussion that follows. 1. The client initiates the negotiation of the SUPPRESS GO AHEAD option. This option starts with a DO since the GO AHEAD command is normally sent by the server to the client, and the client wants the server to enable the option. (This is confusing since enabling the option disables the GA commands from being sent.) The server OKs this option in line 10. 2. The client wants to send its terminal type as specified in RFC 1091 [VanBokkelen 1989]. This is common with Unix clients. This option starts with a WILL since the client wants to enable the option at its end. 3. NAWS stands for "negotiate about window size" and is defined in RFC 1073 [Waitzman 1988]. If the server agrees (which it doesn't, in line II), the client then sends a suboption with the number of rows and columns in the terminal window. Additionally, the client will send this suboption at any time later if the window size changes. (This is similar to what we saw with the Rlogin 0x80 command in Figure 26.4.) 4. The TSPEED option lets the sender (normally the client) send its terminal speed, as defined in RFC 1079 [Hedrick 1988b]. If the server agrees (which it doesn't, in line 12), the client then sends a suboption with its transmit speed and receive speed. 5. LFLOW stands for "local flow control," and is defined in RFC 1372 [Hedrick and Borman 1992]. The client sends this option to the server stating that it is willing to enable and disable flow control on command. If the server a...
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