CS 497C

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CS 497C Introduction to UNIXLecture 35 -
TCP/IP Networking Tools

• Chin-Chih Changchang_at_cs.twsu.edu

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Networking Tools

• talk is a popular network communications program.
• talk charlie
• talk charlie_at_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.

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finger Details of Users

• finger (from Berkeley) is a useful command that
  reveals details of users.
• finger _at_kirk
• finger romeo_at_kirk
• A finger enquiry of a user displays the contents
  of two files, .plan and .project, in the users
  home directory.
• telnet lets you log on to a remote machine by
  supplying a username and password.

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telnet Remote Login

• When telnet is used without the address, the
  system displays the telnetgt 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 Berkeleys implementation of the remote
  login facility, but doesnt require a password.

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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.

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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_at_kiracount.pl calculate.pl

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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.