Bài giảng TCP/IP - Chapter 19: TELNET and Rlogin

Chapter 19TELNETandRloginCONTENTS CONCEPT NETWORK VIRTUAL TERMINAL (NVT) NVT CHARACTER SET EMBEDDING OPTIONS OPTION NEGOTIATION SUBOPTION NEGOTIATION CONTROLLING THE SERVER OUT-OF-BAND SIGNALINGCONTENTS (Continued) ESCAPE CHARACTER MODE OF OPERATION EXAMPLES USER INTERFACE RLOGIN (REMOTE LOGIN) SECURITY ISSUETELNET and Rlogin are general-purpose client-server application programs.CONCEPT19.1Figure 19-1Local loginFigure 19-2Remote loginNETWORKVIRTUALTERMINAL19.2Figure 19-3NVTNVTCHARACTERSET19.3Figure 19-4Format of data charactersFigure 19-5Format of control charactersEMBEDDING19.4Figure 19-6EmbeddingOPTIONS19.5OPTIONNEGOTIATION19.6Figure 19-7Offer to enableFigure 19-8Request to enableFigure 19-9Offer to disableFigure 19-10Request to disableFigure 19-11Echo option exampleSUBOPTIONNEGOTIATION19.7Figure 19-12Example of suboption negotiationCONTROLLINGTHESERVER19.8Figure 19-13Example of interrupting an application programOUT-OF-BANDSIGNALING19.9Figure 19-14Out-of-band signalingESCAPECHARACTER19.10Figure 19-15Two different interruptionsMODEOFOPERATION19.11EXAMPLES19.12Example 1In 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 19.16.Figure 19-16Example1Example 2In 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 19.17.Figure 19-17Example 2USERINTERFACE19.13RLOGIN(REMOTE LOGIN)19.14The Rlogin process uses the TCP port 513.Figure 19-18Connection establishmentFigure 19-19Sending ss command from the client to the serverSECURITYISSUE19.15