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CS 497C – Introduction to UNIX Lecture 35: - TCP/IP Networking Tools

CS 497C – Introduction to UNIX Lecture 35: - TCP/IP Networking Tools. Chin-Chih Chang chang@cs.twsu.edu. TCP/IP Basics. TCP/IP is a set of networking protocols. These protocols define a set of rules that each machine must comply with to communicate with another machine in the network.

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CS 497C – Introduction to UNIX Lecture 35: - TCP/IP Networking Tools

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  1. CS 497C – Introduction to UNIXLecture 35: - TCP/IP Networking Tools Chin-Chih Changchang@cs.twsu.edu

  2. TCP/IP Basics • TCP/IP is a set of networking protocols. • These protocols define a set of rules that each machine must comply with to communicate with another machine in the network. • The term expands to Transmission Control/Internet Protocol. The features of TCP/IP include: • Independence of vendor, type of machine and operating system.

  3. TCP/IP Basics • Independence of vendor, type of machine and operating system. • The delivery of data in multiple packets • Ability to divert data immediately through other routines if one or more parts of the network went down. • One hundred percent reliability of transmission with facilities for full error control. • Unlike the telephone system, TCP/IP is a packet-switching system. In a packet-switched network, there is no dedicated connection.

  4. TCP/IP Basics • The data is broken into packets, and each packet is provided with a header (envelop). • As the packets travel along a vast network like the Internet, they encounter routers. • Routers are special computers or devices that look at the envelope addresses and then determine the most efficient route. • In a network, a computer is known as a host, and every such host has a hostname.

  5. TCP/IP Basics $ hostname • Every host in the network has an address called the IP address. • This address is a series of four dot-delimited members which could typically look like this: 156.26.10.41 • On a small network, the name-address mappings are placed in the file /etc/hosts in every host of the network.

  6. TCP/IP Basics • The Domain Name System (DNS) is a service available in a TCP/IP network which uses the concept of domains and zones to describe uniquely the name of a host in a network. • TCP/IP works in the client-server model. The client application (like ftp) communicates with its server counterpart at the other end to achieve its task.

  7. TCP/IP Basics • The server programs are known as daemons, which run in the background and listen for requests. • The http daemon listens for a Web page request. sendmail is the daemon which handles your mail. • A specific port number is associated with the ftp service, so the packet reaches the ftp server.

  8. TCP/IP Basics • Daemons listen for requests at certain specific port numbers assigned to them. • sendmail listens on port 25, ftp on 21 and telenet on 23. • The port numbers used by the server programs are listed in /etc/services. • Every packet includes a set of four numbers – the IP addresses and TCP port numbers at each end.

  9. Networking Tools • talk is a popular network communications program. talk charlie talk charlie@kirk • Weather you can write or talk depends on the setting of mesg. • The command mesg n prevents other people from writing to a terminal. mesg y enables receipt of such messages.

  10. finger: Details of Users • finger (from Berkeley) is a useful command that reveals details of users. $ finger @kirk $ finger romeo@kirk • A finger enquiry of a user displays the contents of two files, .plan and .project, in the user’s home directory. • telnet lets you log on to a remote machine by supplying a username and password.

  11. telnet: Remote Login • When telnet is used without the address, the system displays the telnet> prompt. • You can now invoke a login session from here with open, close a session with close, log out with logout. • You can do a telnet connection from the Web browser: telnet://kirk.cs.twsu.edu. • rlogin is Berkeley’s implementation of the remote login facility, but doesn’t require a password.

  12. rlogin, ftp $ rlogin kira • rlogin can also be used with the –l option to access other accounts. $ rlogin -l franklin sisko • ftp is used to upload (put and mput) and download (get and mget) files between two hosts. • For the purpose of transfer, files can be seen as belonging to two types – ascii (text) and binary.

  13. ftp: File Transfer Protocol • The name “anonymous” and the email address are used to access an anonymous ftp site. • You can specify a ftp session in a Web browser: ftp://ftp.cs.twsu.edu • rcp can also transfer files but without have to log in. rcp kira:/home/henry/count.pl calculate.pl rcp henry@kira:count.pl calculate.pl

  14. rcp and rsh rcp kira:/home/henry/* rcp –r kira:/home/henry/cgi-bin . • rsh is used in executing a command on a remote machine. rsh kirk ls -l • The r-utilities relogin, rcp, and rsh can only be used if proper authorization is provided at the server end.

  15. Enforcing Security for the Berkeley r-Utilities • System level authorization is controlled by /etc/hosts.equiv. • Authorization can also be enforced at the user level with .rhosts.

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