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Ch4_Network_Utilities.pdf - NETWORK PROGRAMMING Compiled...

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NETWORK PROGRAMMINGCompiled by:Er. Madan KadariyaNCIT
CHAPTER 4:NETWORK UTILITIES AND APPLICATIONNETWORK PROGRAMMING (NP)2
TELNET AND RLOGIN: REMOTE LOGINRemote login is one of the most popular Internet applications. Instead of having a hardwiredterminal on each host, we can login to one host and then remote login across the network to anyother host (that we have an account on, of course).Two popular applications provide remote login across TCP/IP internets.1.Telnetis a standard application that almost every TCP/IP implementation provides. Itworks between hosts that use different operating systems. Telnet uses option negotiationbetween the client and server to determine what features each end can provide.2.Rloginis from Berkeley Unix and was developed to work between Unix systems only, but ithas been ported to other operating systems also.NETWORK PROGRAMMING (NP)3
Remote login uses the client-server paradigm.Fig: Overview of Telnet client-server.NETWORK PROGRAMMING (NP)4
1.The Telnet client interacts with both the user at the terminal and the TCP/IP protocols. Normallyeverything we type is sent across the TCP connection, and everything received from the connection isoutput to our terminal.2.The Telnet server often deals with what's called apseudo-terminaldevice, at least under Unix systems.This makes it appear to the login shell that's invoked on the server, and to any programs run by the loginshell, that they're talking to a terminal device.3.Only a single TCP connection is used. Since there are times when the Telnet client must talk to the Telnetserver (and vice versa) there needs to be some way to delineate commands that are sent across theconnection, versus user data.4.In dashed boxes in Figure to note that the terminal and pseudo terminal drivers, along with the TCP/IPimplementation, are normally part of the operating system kernel. The Telnet client and server, however,are often user applications.5.The login shell on the server host to reiterate that we have to login to the server. We must have anaccount on that system to login to it, using either Telnet or Rlogin.Remote login is not a high-volume data transfer application. Lots of small packets are normally exchangedbetween the two end systems. It is found that the ratio of bytes sent by the client (the user typing at theterminal) to the number of bytes sent back by the server is about 1:20. This is because we type shortcommands that often generate lots of output.NETWORK PROGRAMMING (NP)5
RLOGIN PROTOCOLRlogin appeared with 4.2BSD and was intended for remote login only between Unix hosts. Thismakes it a simpler protocol than Telnet, since option negotiation is not required when the operatingsystem on the client and server are known in advance.

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Term
Fall
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Tags
Transmission Control Protocol, rlogin, NVT

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