1994-99, desktop computing services, rev 4.5b 1 chapter 7 networking perspective of the internet

1 1994-99, Desktop Computing Services, Rev 4.5b

Chapter 7

NetworkingPerspectiveof the Internet


High-Level View

A network of networks Networks in other countries Commercial networks

BitNet, MCI, America OnLine and others National Science Foundation is phasing over to

commercial business Four Network Access Points (NAP)

Sprint, New Jersey PacBell, San Francisco Ameritech, Chicago MFS DataNet, Washington DC


NAP NAP

NAP

NAP

Network Network Network Network Network

Network

Network

ISP HostComputer

YouDialIn

Your Host

Computer

= gateway, router, switch or firewall

You rent spaceYou own the

computer

Architecture


Fundamental Concepts

Connections are varied Dial-up telephone lines Leased lines Fiber-optic Micro-wave links

Design concepts The sender puts data in an Internet Protocol (IP) packet The sender addresses the packet The sender and receiver work together to ensure

accuracy Every computer/device on the network can talk as a peer Hand the packet to a 3rd party provider and they will

move it to my intended destination Platform independent


Domain Names

Domain Names: pickaname.com To the right of the period

.com = commercial .edu = education .gov = government .mil = military .org = anything else .net = network

To the left of the period is the network name A descriptive name picked by the user and approved

by InterNIC (Internet Network Information Center) The country may come just before the period

Example: .ca = Canada .jp = Japan Register through your Internet provider or directly

$70 for the first two years


URLs

Universal Resource Locators First part identifies the protocol or service. For hypertext protocol on the Web

http:// Next comes the server

http://www.psi.net Next is the location on the host computer,

(/directories/filename) http://www.psi.net/promotions/business.html


IP Address Format

IP = Internet Protocol address now administered by Network Solutions (was

Internic) http://www.networksolutions.com dotted-decimal format convention: 129.63.8.108

each dot-delimited section refers to one byte (8 bits) the number between each dot is therefore 0-255 4 bytes = 32 bits theoretically 232 = 4,294,967,296 possible addresses 128-bit IPng (IP Next Generation) addresses are

coming, but there’s no schedule for implementation Identifies the network and the device Use the first 8, 16, or 24 bits to identify the network


Class A: addresses from 0.0.0.0 to 127.0.0.0 first byte is the network part last three bytes are the host address allows 2563 = 16,777,216 addresses on the network

this is a “ludicrously” large number of devices all the free addresses are wasted this class of address is therefore no longer issued

only practical with the use of a net mask which divides the large network into manageable subnets

Class A 07 bits127 networks

24 bits16 million devices0-127

IP Address Classes

Reference: http://www.iu.hioslo.no/~mark/sysadmin/SystemAdmin.html


Class B 1 014 bits16,000 networks

16 bits65,000 devices128-191

IP Address Classes (continued)

Class B: addresses from 128.0.0.0 to 191.255.0.0 first two bytes are the network part last two bytes are the host part allows 2562 = 65,536 addresses on the network typically given to large institutions such as

universities and ISPs (Internet Service Providers)



Class C21 bits2 million networks1 1 0

8 bits254 devices192-223

IP Address Classes (continued)

Class C: addresses from 192.0.0.0 to 233.255.255.0 first three bytes are the network part last byte is the host part allows 2561 = 256 addresses on the network addresses .0 and .255 are reserved by convention



Reserved IP Addresses

1 1 0 Network ID Host ID3 bits 21 bits 8 bits

127.0.0.1 “hard-wired” to localhost (“loopback” address)

90.0.0.n not routable, n can be 0-255 therefore allows 256 local addresses

192.168.a.b also not routable, both a and b can be 0-255 therefore allows 65,536 local addresses

Reference: WinProxy documentation


Connection Service Flavors

connectionless service no delivery confirmation is returned to the sender mail analogy: “send and hope” packets might be duplicated, arrive out of sequence,

or simply be lost and not arrive at all communication via datagrams

connection-oriented service “handshake” confirmation between players telephone analogy: “open a connection” packets can be reassembled exactly as transmitted communication via streams

Reference: Deitel & Deitel, Java How To Program, p. 835


TCP/IP

Actually two separate networking protocols TCP = Transmission Control Protocol

connection-oriented communication via streams

IP = Internet Protocol connectionless communication via datagrams


TCP/IP (continued)

Actually two separate networking protocols TCP = Transmission Control Protocol IP = Internet Protocol

A family of related protocols that provide services E-mail: electronic mail Telnet: remote logon FTP: transfer files (File Transfer Protocol) SMTP: route messages

Simple Mail Transfer Protocol ARP: obtain addresses

Address Resolution Protocol WWW: Connect information using links


TCP/IP (continued)

Actually two separate networking protocols TCP = Transmission Control Protocol IP = Internet Protocol

A family of related protocols that provide services UDP = User Datagram Protocol

a datagram stored inside an IP datagram good for short messages used by Internet Domain

Name Servers (DNS) good for live audio and video where losing single

packets is not critical


Domain Name Service

Maps IP network address numbers to a people- friendly name

A database of domain names Stored at many locations in a hierarchical structure,

not on a central repository Domain names identify specific networks Domain Name Servers look up desired networks in

the database and return their numeric IP addresses Once the packet arrives at the destination network,

it is moved to the host device by the network itself


Domain Name Hierarchy

root domain: unnamed top-level domains: com, edu, gov, org, net, etc. second-level domains: administered by Network

Solutions must be registered on at least two DNS computers primary routes to secondary

third-level domains: added by LAN administratorscs.uml.edu

domain sequence: third.second.top

Reference: Kruglinski, Shepherd, and Wingo, p. 992-993


The HOSTS File relates host names to IP addresses

sort of a mini-DNS DNS not allowed on systems connected to cable modems

due to the volume of traffic they entail on Windows NT: \winnt2\system32\drivers\etc\hosts on Windows 95/98: \windows\hosts

90.0.0.1 reuben2 129.63.1.6 cs90.0.0.2 harold 129.63.1.6 jupiter90.0.0.3 bonnie2 129.63.8.2 saturn90.0.0.4 jroad2 129.63.8.20 dexter90.0.0.7 jroad1 129.63.8.105 martin209.192.194.28 cbtartisan 129.63.8.140 abraham

Reference: Kruglinski, Shepherd, and Wingo, p. 998


Program to Program: Sockets

A combination of the Internet address and Port (application) address IP address: numeric address of the host Port address: address of the application running on

the host or client computer the two together define a socket

Sockets provide a two-way communication channel between applications

Windows Sockets API - ensures that Windows applications can communicate using TCP/IP, regardless of vendor


Unifying Example: Browser Connection

1. Server:listens on port 802. Client:gets server IP address from DNS3. Client:connects to server4. Client:opens 2-way TCP using own port

number5. Client:sends GET request + request headers

GET /filename HTTP/1.1

6. Server:identifies request as a GET & reads headers

7. Server:sends OK response + response headersHTTP/1.1 200 OK

8. Server:sends requested HTML file9. Client:interprets HTML file and displays itReference: Kruglinski, Shepherd, and Wingo, p. 994


Internet Application Architecture

Browserwith JAVA

Machineor Active X

Millions of PCs or “thin clients”

Internet

WebServer

Data Base Server

Data

MerchantServer

Intranetor VPN

CreditCard

TransactionServer

1. Client makes a request

2. Server sends applet back

3. Client uses applet to enter secure transaction

4. Credit is executed

5. Credit company inter- acts with customer and merchant banks


Intranets

Private Internets Use Internet tools Universal clients are in place Use existing LAN wires Use existing WAN

Private leased lines or public switched networks Can use the Internet with encrypting bridges

Sometimes called an “Extranet” Common use: share company information


Security

Internet as an open system Anyone can connect unless you take precautions Encryption (RSA, DES)

Rivest, Shamir, & Adleman (public key encryption technology)

US Digital Encryption Standard Commerce over the Internet

(secure protocols)


Security (continued)

Firewalls Use a router or gateway to filter or control packets Allow only approved IP addresses through A skilled hacker can defeat Many variations exist Example: Firewall-1 from

Checkpoint Technologies About 40% market share http://www.checkpoint.com


Security (continued)

Proxy Servers security efficiency

Internet Service Provider

Modem (phone or cable)

Ethernet Hub gatewaymachine

Reference: http://www2.winproxy.com/support2/setting__up_ln/

1994-99, desktop computing services, rev 4.5b 1 chapter 7 networking perspective of the internet

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