TCPIP Primer

1
TCP/IP Primer

• Brian C. Hoffman
• CINS 142

2
What is TCP/IP

• TCP/IP stands for transmission control protocol /
  Internet protocol.
• A protocol is a set of rules that determine how
  networks communicate with one another.
• TCP/IP is the primary set of protocols that glues
  the Internet together. TCP/IP actually consists
  of several separate protocols of which TCP and IP
  are the most important.

3
Packet Switching

• These protocols work under the concept of packet
  switching.
• Packet switching works as follows
• The data to be sent is broken down into small
  chunks called packets. The maximum packet size is
  65,536 bytes.
• Each packed is labled with a number, the address
  of the sender and destination, and a checksum.
• The packets are trasmitted over the network and
  directed to their destinations by special
  computers called routers.
• One a packet has arrived, the data is
  reconstructed from it and all the other packets.
• For a cute animation see http//www.warriorsofthe.
  net

4
Advantages of TCP/IP and Packet Switching

• TCP/IP is machine, vendor, and operating system
  independent. It is a fixed standard.
• By using packets, the communications line can
  handle multiple different transmissions and is
  not monopolized as with a phone conversation.
• The data can be rerouted if one or more parts of
  the network go down or become congested.
• TCP/IP has full error control and guarantees that
  each packet reaches its destinaton. Packets will
  be resent until the whole message gets through.

5
IP Addresses

• Under the Internet Protocol, ever connected
  computer has a numerical address, an IP address,
  that uniquely identifies it.
• IP addresses take the form ... where each
  number is an eight bit integer. Thus, each number
  must be between 0 and 255.
• Routers use IP addresses to direct a message to
  the destination using tables. Many web site hacks
  have occurred by altering these tables.

6
The Domain Name System

• IP addresses are great for computers, but are
  hard for people to remember. To overcome this,
  the domain name system (DNS) was created.
• The DNS consists of special computers called name
  servers that translate a machine name such as
  student.ccbcmd.edu to a IP address such as
• The /etc/hosts file on the computer can itself be
  used to translate domain names. It is the first
  place the computer checks before going to a DNS
  server.
• A special domain name is localhost. It
  corresponds to an address of 127.0.0.1 and always
  indicates the current computer.

7
DNS Continued

• Domain names follow certain common conventions.
  They are carefully organized into a hierarchy.
• At the highest level is the root domain . (dot)
• Underneath the root you will find the familiar
  categories
• Edu educational institutions
• Com comercial enterprises
• Net networks, usually ISPs or large
  groupings
• Org non-profit organizations
• us country codes us, uk,

8
DNS Continued

• After the main domain, you will find more
  specific information.
• Domain names are written with the most general
  domain at the end and the most specific at the
  front. For example, the schools old name used to
  be student.ccbc.cc.md.us.
• Examining it backwards, we see that
• it is in the us (.us)
• in the state of Maryland (.md.)
• is for a community college (.cc.)
• more specifically, the community college of
  baltimore county (.ccbc.)
• And is for the student computer at that college.
• A name that has all of the proper components is
  called a fully-qualified domain name.

9
Daemons, Ports, and Sockets

• Programs such as ftp or web servers that are
  constantly running are know as daemons. For
  example, httpd listens for web page requests.
• Client programs such as ftp or web browsers
  connect to these daemons for service.
• To distinguish which processes should handle a
  given message, the daemons are assigned ports
  where they listen. Port numbers below 1024
  correspond to well know processes. For example,
  port 80 is used by the web server.
• A socket is an end point for communication and
  consists of an IP address together with a port
  number. No two sockets can have the same address.
  

10
Some Network Commands

• ping
• talk
• finger
• telnet
• ftp
• rlogin
• rsh

11
ping-Checking Your Connection

• The command ping hostname/IP address send packets
  to the provided computer. These packets simply
  request a response. The command then keeps track
  of the total number of packets sent, the number
  of responces, and the response time.
• The ping command can detect if a computer is
  available on the network and can tell you about
  the quality of the connection. The more packets
  lost, the worse the connection.
• Ping is most often used by network technicians to
  help setup and maintain the network. Hackers may
  do a ping sweep to see what IP addresses are
  available on a network.

12
talk- Communicating With Users

• talk usertalk user_at_hostname Allows two users
  to participate in real-time text based
  communication much like an instant messenger or
  chat program.
• Talk is the forerunner of the modern ICQ program,
  but is limited to 2 participants.
• Upon sending a talk request, a user must respond
  with their own talk reply before the communcation
  can start.
• One must enable messages using mesg y to receive
  talk requests.

13
finger-Learning about Users

• ringerfinger userfinger user_at_hostnamefinger
  realname - sometimes giving parts of the real
  name works depending
  on /etc/passwd settings Finger reveals details
  about the user. If no name is supplied it will
  just list all users on the machine.
• Fingering a specific user can give greater
  detail. For example, one can learn what shell
  they are usinf, if they have unread mail, if they
  are allowing messages, and what their plan is.
• To specify your own plan use vi and create a file
  named .plan

14
telnet-Remotely Connecting

• telnet hostnametelnet IP addressTelnet allows
  a user to connect to a remote machine, login, and
  execute commands. The interface is entirely text
  based. Telnet works with a wide number of
  machines.
• rlogin and rsh also allow one to establish a
  remote connection. However, they only work with
  unix machines. If one has the same account name
  on both computers, one may not need to login
  using these commands

15
ftp-Transfering Files

• ftp hostnameftp IP addressFtp allows one to
  connect to a remote machine and transfer files
  using a simple command line interface.
• An ftp session has its own command prompt where
  you can enter commands. Here are some of the most
  common ftp commands
• open
  open connection
• quit
  close connection
• ls
  list remote
• !ls
  list local
• get remote_fname
  get remote file
• put local_fname
  put a local file
• mget remote_fname (wildcards allowed)
  get multiple remote files
• mput locale_fname (wildcards allowed)
  put mutiple local files

16
The Web, Http, and URLs

• The world wide web is the most popular Internet
  application next to email. It allows millions to
  find information and view data in a graphical
  environment.
• The web works using the hypertext transfer
  protocol (http). Http runs on top of the existing
  TCP/IP protocols. It started as a hack of the FTP
  protocol for moving files.
• Web pages and resources are addressed using URLS.
  The general format of a URL is
  protocol//hostname/file_path
• Other protocols supported by most browsers
  include ftp and telnet.