tailieunhanh - Lecture TCP-IP protocol suite - Chapter 19: TELNET and Rlogin

In this chapter you will learn: Concept, network virtual terminal (NVT), NVT character set, embedding, options, option negotiation, suboption negotiation, controlling the server, out-of-band signaling. | Chapter 19 TELNET and Rlogin CONTENTS CONCEPT NETWORK VIRTUAL TERMINAL (NVT) NVT CHARACTER SET EMBEDDING OPTIONS OPTION NEGOTIATION SUBOPTION NEGOTIATION CONTROLLING THE SERVER OUT-OF-BAND SIGNALING CONTENTS (Continued) ESCAPE CHARACTER MODE OF OPERATION EXAMPLES USER INTERFACE RLOGIN (REMOTE LOGIN) SECURITY ISSUE TELNET and Rlogin are general-purpose client-server application programs. CONCEPT Figure 19-1 Local login Figure 19-2 Remote login NETWORK VIRTUAL TERMINAL Figure 19-3 NVT NVT CHARACTER SET Figure 19-4 Format of data characters Figure 19-5 Format of control characters EMBEDDING Figure 19-6 Embedding OPTIONS OPTION NEGOTIATION Figure 19-7 Offer to enable Figure 19-8 Request to enable Figure 19-9 Offer to disable Figure 19-10 Request to disable Figure 19-11 Echo option example SUBOPTION NEGOTIATION Figure 19-12 Example of suboption negotiation CONTROLLING THE SERVER Figure 19-13 Example of interrupting an application program OUT-OF-BAND SIGNALING Figure 19-14 Out-of-band signaling ESCAPE CHARACTER Figure 19-15 Two different interruptions MODE OF OPERATION EXAMPLES Example 1 In this example, we use the default mode to show the concept and its deficiencies even though it is almost obsolete today. The client and the server negotiate the terminal type and terminal speed and then the server checks the login and password of the user. See Figure . Figure 19-16 Example1 Example 2 In this example, we show how the client switches to the character mode. This requires that the client request the server to enable the SUPPRESS GO AHEAD and ECHO options. See Figure . Figure 19-17 Example 2 USER INTERFACE RLOGIN (REMOTE LOGIN) The Rlogin process uses the TCP port 513. Figure 19-18 Connection establishment Figure 19-19 Sending ss command from the client to the server SECURITY ISSUE | Chapter 19 TELNET and Rlogin CONTENTS CONCEPT NETWORK VIRTUAL TERMINAL (NVT) NVT CHARACTER SET EMBEDDING OPTIONS OPTION NEGOTIATION SUBOPTION NEGOTIATION CONTROLLING THE SERVER OUT-OF-BAND SIGNALING CONTENTS (Continued) ESCAPE CHARACTER MODE OF OPERATION EXAMPLES USER INTERFACE RLOGIN (REMOTE LOGIN) SECURITY ISSUE TELNET and Rlogin are general-purpose client-server application programs. CONCEPT Figure 19-1 Local login Figure 19-2 Remote login NETWORK VIRTUAL TERMINAL Figure 19-3 NVT NVT CHARACTER SET Figure 19-4 Format of data characters Figure 19-5 Format of control characters EMBEDDING Figure 19-6 Embedding OPTIONS OPTION NEGOTIATION Figure 19-7 Offer to enable Figure 19-8 Request to enable Figure 19-9 Offer to disable Figure 19-10 Request to disable Figure 19-11 Echo option example SUBOPTION NEGOTIATION Figure 19-12 Example of suboption negotiation CONTROLLING THE SERVER Figure 19-13 Example of interrupting an application program .