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CIT 140: Introduction to IT. Networking. Topics. What are Networks? Why do we want Networks? Social Issues Sizes and Types of Networks Circuit vs Packet Switching Network Structures: Peer-to-peer and Client-server Performance Issues Network Protocols and Models TCP/IP

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Cit 140 introduction to it

CIT 140: Introduction to IT

Networking

CIT 140: Introduction to IT


Topics

Topics

  • What are Networks?

  • Why do we want Networks?

  • Social Issues

  • Sizes and Types of Networks

  • Circuit vs Packet Switching

  • Network Structures: Peer-to-peer and Client-server

  • Performance Issues

  • Network Protocols and Models

  • TCP/IP

  • History of Networks

  • UNIX Network Commands

CIT 140: Introduction to IT


What is a computer network

What is a Computer Network?

When two or more computer hardware resources are connected they form a computer network.

CIT 140: Introduction to IT


Why networks

Why Networks?

Resource Sharing

Physical resources: printers, scanners, faxes

Information: files, databases, web pages

Communication

E-mail

Collaborative work

E-commerce

Instant messaging

CIT 140: Introduction to IT


Social issues

Social Issues

Controversial topics

Politics, religion, sex

Employers vs employees

Monitoring

Censorship

Government vs citizens

FBI Carnivore System

National Security Letters

CIT 140: Introduction to IT


Sizes of networks

Sizes of Networks

PANs: Personal Area Networks

LANs: Local Area Networks

WLANs: Wireless LANs

MANs: Metropolitan Area networks

WANs: Wide Area networks

CIT 140: Introduction to IT


Types of networks

Types of Networks

Subnetworks are parts of individual networks, often connected through a single switch.

Network can refer to any size network.

Internetworks are larger networks composed of multiple networks.

CIT 140: Introduction to IT


Cit 140 introduction to it

Computer Networks and Internetworks

CIT 140: Introduction to IT


Circuit vs packet switching

Circuit vs Packet Switching

Circuit-switched: A connection called a circuit is set up between two devices and used for the whole communication.

Packet-switched: Data is chopped up into small pieces called packets and sent over the network. Each packet may follow a different path between the communicating parties.

CIT 140: Introduction to IT


Circuit vs packet switching1

Circuit vs Packet Switching

CIT 140: Introduction to IT


Network structure

Network Structure

Peer-to-Peer: Every computer is an equal peer, running similar software with no special roles. Requests can be from any computer to any other computer.

Client-Server: A small number of computers are designed as central servers to provide services to a larger number of user machines called clients.

CIT 140: Introduction to IT


Client server computing

Client/Server Computing

CIT 140: Introduction to IT


Performance issues

Performance Issues

Throughput

  • Amount of data that can be sent per unit time.

  • ex: 56Kbps cable modem

  • ex: 4000Kbps cable modem

    Latency

  • Amount of time from request to response.

  • ex: 2 PCs on a network have a latency ~ 10ms

  • ex: Satellite internet has a latency ~1000ms

CIT 140: Introduction to IT


Throughput vs latency

Throughput vs Latency

An Ultrium3 tape holds 400GB.

A 60cm3 box holds 100 tapes.

The box contains 3200 terabits!

FedEx can ship it anywhere in US in 24 hrs.

Throughput is 3200 terabits / 86400 seconds

= 38 Gbps!

NetFlix transfers more data than Internet!

Latench is 24 hours though.

CIT 140: Introduction to IT


Network protocols

Network Protocols

A protocol is an agreement between communicating parties on how communication is to proceed.

CIT 140: Introduction to IT


Protocol example http

Protocol Example: HTTP

> telnet www.google.com 80

Trying 72.14.203.99...

Connected to www.l.google.com.

Escape character is '^]'.

GET / HTTP/1.1

HTTP/1.1 200 OK

Cache-Control: private

Content-Type: text/html

Set-Cookie: PREF=ID=e812e6c7ead517fe:TM=1131846389:LM=1131846389:S=rD8-WNplszt1Ko8A; expires=Sun, 17-Jan-2038 19:14:07 GMT; path=/; domain=.google.com

Server: GWS/2.1

Transfer-Encoding: chunked

Date: Sun, 13 Nov 2005 01:46:29 GMT

a46

<html><head><meta http-equiv="content-type" content="text/html; charset=ISO-8859-1"><title>Google</title><style>

CIT 140: Introduction to IT


Protocol example http1

Protocol Example: HTTP

> telnet www.google.com 80

Trying 72.14.203.99...

Connected to www.l.google.com.

Escape character is '^]'.

GET /foo HTTP/1.1

HTTP/1.1 404 Not Found

Content-Type: text/html

Server: GWS/2.1

Content-Length: 1244

Date: Sun, 13 Nov 2005 01:47:47 GMT

CIT 140: Introduction to IT


Protocol stacks

Protocol Stacks

Protocols are stacked together in layers

High level protocols are application protocols.

Medium level ones perform tasks like routing packets through the network.

Low level protocols deal with cabling and electrical signaling.

CIT 140: Introduction to IT


Cit 140 introduction to it

Network Models

CIT 140: Introduction to IT


Application layer

Application Layer

User applications

  • Web (http)

  • E-mail (smtp)

CIT 140: Introduction to IT


Transport layer

Transport Layer

The transport layer is an end-to-end protocol that transports application data from your machine to a remote machine and vice versa.

User Datagram Protocol(UDP) offers the best effort delivery service.

Transmission Control Protocol (TCP) offers the completely reliable, in-sequence delivery. It provides a virtual circuit for the communication.

CIT 140: Introduction to IT


Network layer

Network Layer

IP protocol routes packets from source to destination.

Uses IP addresses for source and destination.

ex: 10.11.32.10

Does not guarantee delivery.

Responsibility of transport or application layer.

Uses special purpose computers called routers.

CIT 140: Introduction to IT


Ip routing

IP Routing

CIT 140: Introduction to IT


Ip addresses

IP Addresses

32-bit binary numbers

IP addresses are given in dotted decimal notation (DDN)

> ifconfig hme0

hme0: flags=1000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4> mtu 1500 index 2

inet 172.20.20.40 netmask ffffff00 broadcast 172.20.20.255

CIT 140: Introduction to IT


Dns names

DNS Names

Symbolic names are easier to remember

Remain same even if the numeric address changes

Must be unique for a host on the Internet

Format: hostname.domain_name

Example: www.nku.edu

mail.nku.edu

cs.nku.edu

CIT 140: Introduction to IT


The domain name system

The Domain Name System

Domain Name System (DNS) translates DNS names from application layer to IP addresses for network layer.

DNS implements a distributed database of name-to-address mappings.

A set of dedicated hosts run name servers that take requests from the application software and work together to map domain names to the corresponding IP addresses

CIT 140: Introduction to IT


Cit 140 introduction to it

The Domain Name System

CIT 140: Introduction to IT


Dig dns lookup

Dig: DNS Lookup

dig [options]

PurposeInteract with name servers specified in/etc/resolv.conf and display their responses

OutputResponses of name servers for queries sent to them

Commonly used option/features:

-f fileFor batch operation , take domain names (or IP addresses) from ‘file

-p portInteract with a name server at ‘port’ instead of the default port53

CIT 140: Introduction to IT


Dig example

Dig Example

> dig www.google.com

; <<>> DiG 8.3 <<>> www.google.com

;; res options: init recurs defnam dnsrch

;; got answer:

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2

;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 5, ADDITIONAL: 0

;; QUERY SECTION:

;; www.google.com, type = A, class = IN

;; ANSWER SECTION:

www.google.com. 14m40s IN CNAME www.l.google.com.

www.l.google.com. 4m40s IN A 72.14.203.104

www.l.google.com. 4m40s IN A 72.14.203.99

CIT 140: Introduction to IT


Data link layer

Data Link Layer

Break up transmission into small enough packets (often called frames) and send them sequentially.

Traffic regulation: ensure fast transmitter doesn’t overwhelm slow receiver.

CIT 140: Introduction to IT


Physical layer

Physical Layer

How many volts is a 1?

How many volts is a 0?

How long does a bit last?

How many pins does connector have?

What is each pin used for?

CIT 140: Introduction to IT


Internet standards

Internet Standards

IETF (Internet Engineering Task Force)

  • Open group responsible for Internet standards.

    RFC (Request for Comments)

  • Internet standard documents.

  • IETF archives RFCs at www.ietf.org.

    IANA (Internet Assigned Numbers Authority)

  • Coordinates unique network numbers.

  • IP addresses, protocol numbers, etc.

    ICANN (Inet. Corp. for Assigned Names & Numbers)

  • Manages DNS top level domains (TLDs) like .com, .gov

  • Gives domain registrars responsibilities over domains.

CIT 140: Introduction to IT


History of internet

History of Internet

1969 ARPAnet created (4 hosts)

1984 DNS deployed

1986 Cleveland Freenet offers free Internet access

1987 Number of hosts reaches 10,000

1988 Morris Worm

1989 Number of hosts reaches 100,000

1990 First commercial dialup ISP

1991 WWW released at CERN

1992 Number of hosts reaches 1,000,000

1993 Mosaic, graphical web browser, released

1994 First banner ads appear on the web

1995 AOL offers Internet access

1996 Telcos try to ban Internet telephones

1996 Number of hosts reaches 10,000,000

2000 Number of hosts reaches 100,000,000

CIT 140: Introduction to IT


Displaying the hostname

Displaying the Hostname

> hostname

zappa

> uname -n

zappa

> uname -a

SunOS zappa 5.9 Generic_112233-07 sun4u sparc SUNW,Ultra-250

CIT 140: Introduction to IT


Testing a network connection

Testing a Network Connection

ping [options] hostname

Purpose: Send packet to hostname. If hostname is up, packet is echo’ed back and ping records that host is alive.

Commonly used options/features:

-s Send one packet/second andrecord latency statistics.

CIT 140: Introduction to IT


Ping example

Ping Example

> ping www.uc.edu

no answer from www.uc.edu

> ping www.google.com

www.google.com is alive

> ping -s www.google.com

PING www.google.com: 56 data bytes

64 bytes from 72.14.203.104: icmp_seq=0. time=17. ms

64 bytes from 72.14.203.104: icmp_seq=1. time=20. ms

64 bytes from 72.14.203.104: icmp_seq=2. time=17. ms

64 bytes from 72.14.203.104: icmp_seq=3. time=21. ms

64 bytes from 72.14.203.104: icmp_seq=4. time=16. ms

^C

----www.google.com PING Statistics----

5 packets transmitted, 5 packets received, 0% packet loss

round-trip (ms) min/avg/max = 16/18/21

> ping -s www.muohio.edu

PING www.muohio.edu: 56 data bytes

64 bytes from w8zr.net (134.53.7.73): icmp_seq=0. time=43. ms

64 bytes from w8zr.net (134.53.7.73): icmp_seq=1. time=1260. ms

64 bytes from w8zr.net (134.53.7.73): icmp_seq=2. time=263. ms

64 bytes from w8zr.net (134.53.7.73): icmp_seq=3. time=43. ms

64 bytes from w8zr.net (134.53.7.73): icmp_seq=4. time=42. ms

^C

----www.muohio.edu PING Statistics----

5 packets transmitted, 5 packets received, 0% packet loss

round-trip (ms) min/avg/max = 42/330/1260

CIT 140: Introduction to IT


Traceroute

Traceroute

> traceroute www.google.com

traceroute: Warning: www.l.google.com has multiple addresses; using 72.14.203.104

traceroute to www.l.google.com (72.14.203.104), 30 hops max, 40 byte packets

1 172.20.20.253 (172.20.20.253) 0.550 ms 0.332 ms 0.307 ms

2 192.122.237.10 (192.122.237.10) 0.715 ms 0.690 ms 0.731 ms

3 h13.188.140.67.ip.alltel.net (67.140.188.13) 1.234 ms 1.192 ms 1.066 ms

4 h6.31.213.151.ip.alltel.net (151.213.31.6) 3.515 ms 3.710 ms 3.705 ms

5 h212.33.213.151.ip.alltel.net (151.213.33.212) 3.547 ms 3.491 ms h208.33.213.151.ip.alltel.net (151.213.33.208) 3.558 ms

6 so-1-0.hsa2.Cincinnati1.Level3.net (4.78.218.5) 5.506 ms 29.589 ms 12.175 ms

7 4.68.124.241 (4.68.124.241) 6.038 ms ae-1-54.bbr2.Chicago1.Level3.net (4.68.101.97) 62.243 ms 19.935 ms

8 4.68.124.202 (4.68.124.202) 19.798 ms 19.855 ms so-2-0-1.bbr2.Chicago1.Level3.net (64.159.0.162) 16.263 ms

9 francetelecom-level3-oc48.Chicago1.Level3.net (4.68.111.2) 19.930 ms 4.68.124.202 (4.68.124.202) 15.908 ms francetelecom-level3-oc48.Chicago1.Level3.net (4.68.111.2) 19.779 ms

10 * * *

11 66.249.95.253 (66.249.95.253) 20.204 ms * *

12 72.14.238.89 (72.14.238.89) 20.886 ms 66.249.95.253 (66.249.95.253) 16.119 ms 16.023 ms

13 72.14.238.89 (72.14.238.89) 17.237 ms 16.971 ms 17.030 ms

14 72.14.203.104 (72.14.203.104) 21.288 ms 64.233.175.94 (64.233.175.94) 19.653 ms 27.886 ms

CIT 140: Introduction to IT


Displaying user information

Displaying User Information

finger [options] [user_list]

Purpose: Display information about the users in the ‘user_list’; without a ‘user_list’, the command displays a short status report about all the users currently logged on to the specified hosts

Output: User information extracted from the ~/.project and ~/.plan files

Commonly used options/features:

-mMatch ‘user_list’ to login names only

-sDisplay output in a short format.

CIT 140: Introduction to IT


Finger example

Finger Example

> finger waldenj

Login name: waldenj

Directory: /export/home0/waldenj Shell: /bin/bash

On since Nov 13 09:39:18 on pts/2 from 23.112.19.41

No unread mail

Plan:

Fall 2005 Class Schedule

CSC 382 Computer Security MW 1:40-2:55

CIT 140 Introduction to IT TR 2:00-3:15

CSC 501 Int. Prog. Workshop TR 4:50-6:05

> finger -s waldenj

Login Name TTY Idle When Where

waldenj ??? pts/2 Sun 09:39 23.112.19.41

CIT 140: Introduction to IT


Remote login telnet obsolete

Remote Login: telnet (Obsolete)

telnet host [port]

Purpose: Obsolete, insecure protocol for logging into a remote system. Superseded by ssh.

Currently used to demonstrate network protocols by connecting to their ports, as we did for HTTP earlier.

Ports for common protocols are listed in the file /etc/services.

CIT 140: Introduction to IT


Telnet port example 80

Telnet Port Example: 80

> telnet www.google.com 80

Trying 72.14.203.99...

Connected to www.l.google.com.

Escape character is '^]'.

GET /foo HTTP/1.1

HTTP/1.1 404 Not Found

Content-Type: text/html

Server: GWS/2.1

Content-Length: 1244

Date: Sun, 13 Nov 2005 01:47:47 GMT

CIT 140: Introduction to IT


Remote login ssh

Remote Login: ssh

ssh [options] host [command]

ssh [options] [email protected] [command]

Purpose: Secure login to remote host.

Commonly used options/features:

-l userLogin as specified username.

-p portSpecifies remote port to connect to

-vVerbose output

CIT 140: Introduction to IT


Ssh secure shell

ssh: secure shell

> ssh [email protected] who

Password:

jw :0 Oct 15 14:11

jw pts/0 Nov 10 08:58 (:0.0)

jw pts/1 Oct 22 12:46 (:0.0)

jw pts/2 Oct 21 23:02 (:0.0)

jw pts/7 Oct 15 14:20 (:0.0)

> ssh [email protected] "ps -ef | grep ssh"

Password:

jw 7779 7733 0 Oct15 ? 00:00:00 /usr/bin/ssh-agent /usr/bin/dbus-launch --exit-with-session /usr/bin/gnome-session

root 1890 1 0 Oct21 ? 00:00:02 /usr/sbin/sshd

root 5882 1890 0 Nov10 ? 00:00:00 sshd: jw [priv]

jw 5886 5882 0 Nov10 ? 00:00:00 sshd: [email protected]

jw 25660 25659 0 21:49 ? 00:00:00 bash -c ps -ef | grep ssh

jw 25674 25660 0 21:49 ? 00:00:00 grep ssh

CIT 140: Introduction to IT


The scp command

The scp Command

Securely copy files from machine to machine across the network

> scp prog.c zappa.nku.edu:~/classes/cit140/programs/

Password:

> scp -r zappa.nku.edu:classeses .

Password:

CIT 140: Introduction to IT


The sftp command

The sftp Command

Securely copy files from machine to machine across the network using an interactive session.

> sftp [email protected]

Connecting to zappa.nku.edu...

[email protected]'s password:

sftp> ls

bash-3.0.tar.gz cit140 csc382

csc501 mailpublic_html

sftp> get bash-3.0.tar.gz

Fetching /export/home0/waldenj/bash-3.0.tar.gz to bash-3.0.tar.gz

/export/home0/waldenj/bash-3.0.tar.gz 100% 2362KB 472.3KB/s 00:05

sftp> quit

CIT 140: Introduction to IT


File transfer

File Transfer

ftp [options] [host]

Purpose:To transfer files from or to a remote machine.

Commonly used options/features

-dEnable debugging

-iDisable prompting during transfers of multiple files

-vShow all remote responses

CIT 140: Introduction to IT


Ftp example

FTP Example

> ftp ftp.gnu.org

Connected to ftp.gnu.org.

220 GNU FTP server ready.

Name (ftp.gnu.org:waldenj): ftp

230-Due to U.S. Export Regulations, all cryptographic software on this

230-site is subject to the following legal notice:

230 Login successful.

Remote system type is UNIX.

Using binary mode to transfer files.

ftp> cd gnu/bash

250 Directory successfully changed.

ftp> dir bash-3.0*

200 PORT command successful. Consider using PASV.

150 Here comes the directory listing.

drwxr-xr-x 2 1003 1003 4096 Feb 14 2005 bash-3.0-patches

-rw-r--r-- 1 1003 65534 2418293 Aug 03 2004 bash-3.0.tar.gz

-rw-r--r-- 1 1003 65534 65 Aug 03 2004 bash-3.0.tar.gz.sig

226 Directory send OK.

remote: bash-3.0*

224 bytes received in 0.0074 seconds (29.39 Kbytes/s)

CIT 140: Introduction to IT


Automating ftp

Automating Ftp

> wget ftp://ftp.gnu.org/gnu/bash/bash-3.0.tar.gz

--21:42:24-- ftp://ftp.gnu.org/gnu/bash/bash-3.0.tar.gz

=> `bash-3.0.tar.gz'

Resolving ftp.gnu.org... done.

Connecting to ftp.gnu.org[199.232.41.7]:21... connected.

Logging in as anonymous ... Logged in!

==> SYST ... done. ==> PWD ... done.

==> TYPE I ... done. ==> CWD /gnu/bash ... done.

==> PORT ... done. ==> RETR bash-3.0.tar.gz ... done.

Length: 2,418,293 (unauthoritative)

100%[====================================>] 2,418,293 579.54K/s ETA 00:00

21:42:29 (579.54 KB/s) - `bash-3.0.tar.gz' saved [2418293]

CIT 140: Introduction to IT


Automating web transfers

Automating Web Transfers

> wget http://greenend.org.uk/~sgtatham/putty/latest/x86/putty.exe

--21:44:51--http://greenend.org.uk/~sgtatham/putty/latest/x86/putty.exe

=> `putty.exe'

Location: http://the.earth.li/~sgtatham/putty/0.58/x86/putty.exe [following]

--21:44:52-- http://the.earth.li/%7Esgtatham/putty/0.58/x86/putty.exe

=> `putty.exe'

Connecting to the.earth.li[193.201.200.66]:80... connected.

HTTP request sent, awaiting response... 200 OK

Length: 421,888 [application/x-msdos-program]

100%[====================================>] 421,888 307.46K/s ETA 00:00

21:44:54 (307.46 KB/s) - `putty.exe' saved [421888/421888]

CIT 140: Introduction to IT


Interactive chat

Interactive Chat

talk user

Purpose: to initiate interactive chat with user who is logged in on a specific terminal

> talk bob

[Waiting for your party to respond]

Message from [email protected] at 13:36 ...

talk: connection requested by [email protected]

talk: respond with: talk [email protected]

> talk [email protected]

CIT 140: Introduction to IT


  • Login