65890396 internet programming tools

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Internet Programming ToolsWhat Is the Internet?

A network of networks, joining many government, university and private computers

together and providing an infrastructure for the use of E-mail, bulletin boards, file archives,

hypertext documents, databases and other computational resources

The vast collection of computer networks which form and act as a single huge network for

transport of data and messages across distances which can be anywhere from the sameoffice to anywhere in the world.

What is the Internet?

1. The largest network of networks in the world.

2. Uses TCP/IP protocols and packet switching .

3. Runs on any communications substrate.

Brief History of the Internet

1968 - DARPA (Defense Advanced Research Projects Agency) contracts with BBN (Bolt,

Beranek & Newman) to create ARPAnet. The funds were provided by the Department of

Defense(DoD) in 1969.

1970 - First five nodes:

a. UCLA

b. Stanfordc. UC Santa Barbara

d. U of Utah, and

e. BBN

1974 - TCP specification by Vint Cerf

1984 On January 1, the Internet with its 1000 hosts converts en masse to using TCP/IP

for its messaging

Internet Growth Trends

i. 1977: 111 hosts on Internet

ii. 1981: 213 hosts

iii. 1983: 562 hosts

iv. 1984: 1,000 hostsv. 1986: 5,000 hosts

vi. 1987: 10,000 hosts

vii. 1989: 100,000 hostsviii. 1992: 1,000,000 hosts

ix. 2001: 150 175 million hosts

x. 2002: over 200 million hostsxi. By 2010, about 80% of the planet will be on the Internet


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Internet Addressing

i. Addresses provide information on how to locate something, e.g., what route to take fromhere to there.

ii. Internet addresses combine

a. a routing portion, known as the network partb. a name portion known as the host part

iii. How to split an Internet address into the network part and the host part has changed over

timeiv. Back when the TCP/IP protocols were first being designed, there was a big argument

between fixed length and variable length addresses

a. Fixed length will always be limited

i. But if you make it big enough, no one will noticeb. Variable length will always take more cycles to process

i. But there are tricks you can play to minimize the difference

v. The decision was made for fixed, 32 bit addresses

IP Address

a. An IP address is a 32-bit sequence of 1s and 0s.b. To make the IP address easier to use, the address is usually written as four decimal

numbers separated by periods.

c. This way of writing the address is called the dotted decimal format.

d.

e.

Every IP address has two parts:

Network

IP addresses are divided intoclasses A,B and C to definelarge, medium, and smallnetworks.

Host

The Class D address class

was created to enable

multicasting.

IETFreserves Class E

addresses for its own

research.


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Reserved IP Addresses

a. Certain host addresses are reserved and cannot be assigned to devices on a network.b. An IP address that has binary 0s in all host bit positions is reserved for the network

address.

c. An IP address that has binary 1s in all host bit positions is reserved for the broadcast

address.

Obtaining an Internet Network Address

a. IP network addresses must be unique, or the Internet will not be stable

b. The Internet Network Information Centre (InterNIC) was originally responsible for

issuing Internet network addressesc. Today, the Internet Assigned Number Authority (IANA) issues network addresses to

Information Service Providers (ISPs)

d. ISPs split networks up into subnets and sell them on to their customers

Text Internet Addressing

i. In text Internet addresses, the text strings are referred to as Domainsii. Every internet mail address has two parts, they are separated by @ sign.

a. Username

b. Name of the Internet Provider


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iii. The domain for the providers ends with the zone. Some of the Zones are

iv.

v. jstewar [email protected]&l.com.uk

a. Th

etop

level domain shows which country the computer is located in,b. The second level domain indicates the type of organization.

c. Between Second and user name there might be several intermediate domains that

locate an organization.

OSI Model

OSI Layers

.com Commercial Organization

.edu Educational Institutions

.net Networking Organizations

.gov US Government Sites

.mil Military sites

.org Other Organizations


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Physical layers - The physical layer is responsible for the movement of individual bits from onehop (node) to the next.


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Data Link layer - The data link layer is responsible for moving frames from one hop (node) tothe next.


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HOP TO HOP DELIVERY

Network Layer - The network layer is responsible for the delivery of individual packets fromthe source host to the destination host

Source to Destination Delivery


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Transport layer - The transport layer is responsible for the delivery of a message from oneprocess to another.

Reliable process-to-process delivery of a message

Session Layer

Presentation Layer


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Application Layer

Summary of Layers

TCP/IP Protocol Suite

The TCP/IP protocol suite is made of five layers: physical, data link, network, transport, andapplication. The first four layers provide physical standards, network interface,

internetworking, and transport functions that correspond to the first four layers of the OSI


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model. The three topmost layers in the OSI model, however, are represented in TCP/IP by

a single layer called the application layer.

Addressing

Three different levels of addresses are used in an internet using the TCP/IP protocols: physical

(link) address, logical (IP) address, and

port address.

Addresses in TCP?IP Relationship of Layers


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DNS Overview

What is DNS? Distributed Directory Service

Maps names to values resource records

Highly resilient to attack* Major backbone of the internet

Makes networks human friendly

Defined (primarily) in RFC1034 and 1035

*if implemented properly

DNS vs File System

What is a domain?

A domain is a sub tree of a larger tree identified by a domain name

Contains resource records and sub-domains Some resource records point to authoritative server for sub-domains / zones

eg. the root contains pointers to .au

google.com.au is a domain

com net au info biz

com net

org

org

Other

ccTLDs

id

internal prosrs

google yahoo theagemicrosoftausregistry

c o m n e ta u

c o m n e to r g id

g o o g le y a h o om ic ro s o f t

C :

P ro gra m

F ile sT e m pW i n d o w s

S y s te m 3 2 F o n tsC a c h e M e d ia

d l lc a c h e s p o o ld riv e rs

c o m n e t a u in fo b iz

c o m n e t

o rg

o rg

O th e r

c c T L D s

id

in te rn a l p ro s rs

g o o g l e y a h o o t h e a g em ic ro so fta u s re g is tr y


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What is a resource record?

A domain contains resource records

Resource records are analogous to files Classified into types

Some of the important types are SOA, NS, A, CNAME and MX

Normally defines in zone files

Type Meaning Value

SOA Start of Authority Parameters for this zone

A IP address of a host 32bit integer

MX Mail Exchange Priority, domainwilling to accept email

CNAME Canonical Name Domain Name

PTR Pointer Alias for an IP address

HINFO Host Description CPU and OS in ASCII(security risk rarely used)

TXT Text Uninterpreted ASCII text

Domain Names vs. URLs

The A Record

The Address record

One or more normally defines a host

Contains an IPv4 Address (the address computers use to uniquely identify each other onthe internet)

Eg. The record:

www A 203.18.56.31In the ausregistry.com.au domain, defines the host uniquely identifiable as

www.ausregistry.com.au to be reachable at the IPv4 Address 203.18.56.31

The CNAME Record

A CNAME defines an alias

The alias will then be resolved, if another CNAME is encountered then the process

continues until an A record is found

Eg. The record:search CNAME www.google.com.

In the ausregistry.com.au domain, defines the name uniquely identifiable as

search.ausregistry.com.au to be and alias to www.google.com

The MX Record

An MX record defines the mail servers for a particular domain Mail eXchange records hold the name of hosts, and their priorities, able to deliver mail

for the domain.

Eg. The record:

ausregistry.com.au MX 10 mail
http://www.google.com/http://www.google.com/


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In the ausregistry.com.au domain, defines the host mail to be the priority 10 mail server for the

ausregistry.com.au domain

The NS Record

An NS record defines the authoritative Name servers for the domain.

The Name Server records also define the name servers of children domains Eg. The record:

internal NS ns1.hosting.com.au.

In the ausregistry.com.au domain, defines the host ns1.hosting.com.au to be a name severfor the internal.ausregistry.com.au sub-domain

What is a Delegation?

Delegation refers to the act of putting NS records in a domain name delegating controlof a sub-domain to another entity

This entity then has the ability to control the resource records in this sub-domain and

delegate further children domains to other entities.

Eg. IANA delegating control of a country code domain to the country.

What is a zone?

Its records are held in a database (zonefile) and served from an authoritative name

server

Zone refers to all the resource records in a domain but not its sub domains, the com.au zonecontains delegations records for ausregistry.com.au, but not the resource records for

ausregistry.com.au, however all of these records are part of the com.au domain

What is a Name Sever?

Server responsible for answering DNS queries

Exists at all levels of hierarchy

Authoritative name servers hold part of the DNS database One name server can serve more then one zone

Many name servers should serve the same zone

Some name servers are authoritative for certain zones

Iterative vs Recursive Name Servers

Serve two very different functions

Shouldnt mix the two Generally the DNS your computer points to is recursive

Zones are hosted in iterative name servers

Iterative servers can only answer information they know or have cachedRecursive know how to ask others for information

Who runs what?

ICANN/IANA have been granted the power by the US department of commerce to run

the root zone.

Root zone is split into all the ISO ccTLD and some other TLDs eg. .com, .net, .info

Domain name Registries are appointed to operate the major zones.


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Each country elects a delegate whom controls their ccTLD eg in Australia the delegate is

auDA.

Modify TLD and ccTLD resource records on behalf of registrants through a system of registrarseg. MelbourneIT.

So what does all this mean to you? Domain names make large networks such as the internet human friendly

IPv4 address difficult to remember and offer no hint as to whom they belong to.

Problem gets worse when you consider IPv6Allow intelligent systems (eg Mail (SMTP)) to preform tasks automaticall

Accessing a web page

Step 1: Your PC sends a resolution

request to its configured DNS

Server, typically at your ISP.

Your PC

ISP Recursive DNS server

Tell methe Address of

www.google.com

ISP Recursive DNSserverRoot Servers

Step 2: Your ISPs recursive name

server starts by asking one of the

root servers predefined in its hints

file.Tell methe Addressofwww.google.com

I dont knowthe address but I

knowwhos authoritative for the

com domain askthem

ISPRecursive DNSservercom DNSservers


server then asks one of the comname servers as directed.Tell me the Addressof

www.google.com

I dont knowthe addressbut Iknowwhos authoritativefor thegoogle.com domainaskthem

ISP Re cursive DNS server google.com DNS server


server then asks one of thegoogle.com name servers as

directed.Tell me theAddressofwww.google.com

The Address of www.google.com

is216.239.53.99

Step 5: ISP DNS server then send

the answer back to your PC. TheDNS server will remember the

answer for a period of time.

Your PC

ISPRecursive DNSserver

The Addressof www.google.comis 216.239.53.99

Step 6: Your PC can then make the

actual HTTP request to the webserver.

Your PC

www.google.comweb server

Here it is!

Sendmethe www.google.com.auwebpage


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Summary

ISP Recursive DNS server com DNS servers

root DNS servers

google.com DNS server

3

2

4

Your PC

5

1

google.com.au

Web Server

WEB (HTTP)

Request

DNSr equests

6

The actual

web requestDNS

Sending an Email

DNS is not just used in HTTP protocol (web pages)

DNS is involved in almost every protocol in use on the internet Next example is how DNS facilitates the transfer of electronic mail.

Step 1: Your PC sends the e -mail

to its configured outbound mail

server. ADNS request similar to the

previous example is required to find

the address of the mail server.

Your PC

Outbound Mail (SMTP) Server

Pleasesend thismessage to

[email protected]

Outbound Mail serverDNSservers

Step 2: Your mail server follows

the same intensive process to find

the authoritative servers for

example.com.Tell me the name servers for

example.com

Here are the name servers for

example.com

Outbound Mail Server example.com DNS server

Step 3: Ask the example.com

name server for the list of Mail

eXchangers (MX) for that domain.

Tell me the MXsfor

example.com

The MXsare mx10.example.com

and mx20.backmail.com

Outbound Mail Server example.com Mail server

Step 4: Select a Mail server anddeliver the mail.

Here issome mail for theexample.comdomain

Mail acceptedfor delivery

Summary

DNS is integral part in most protocols used on the internet Makes the internet human friendly for us all

Is the world largest distributed database system

Fits the international model perfectlyIn simple terms is a mapping between names and IP addresses

What is E-mail?

E-mail is a text-based mail sent via the computer from one person to another.


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E-mail is an ideal method for sending documents already on your computer usingattachments.

In computer terms, email is short for electronic mail. It is a more up to date method oftransmitting data, text files, and digital photos and ... from one computer to another over the

Internet. This phenomenon did not become popular until 1990 and now it is a major business and

personal communications.

Email users create and send messages from individual computers using Mail-User Agents

(MUAs).

If the user were to send the message to more than one recipient, it is called broadcasting.

An E-mail account may looks like below:

[email protected] [email protected]

user@computername [email protected]

Two Important Mail Protocols

Two important protocols

Mail Process

POP3: Is useful when e-mail is checked from only one computer.

POP3 works by reviewing the inbox on the mail server, and downloading the newmessages to your computer so your mail is stored on your PC.

IMAP is the better choice when you would like to check your mails from multiple

computers at work and home.

IMAP downloads the headers of the new messages on the server, then retrieves the

message you want to read when you click on it.

When using IMAP, the mail is stored on the mail server. Unless you copy a message to a

"Local Folder" the messages are never copied to your PC.

Scenarios of Use

POP3:

You only check e-mail from one computer.

You want to remove your e-mail from the mail server.


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IMAP:

You check e-mail from multiple locations.

You use Webmail.

Mail process:

MUA: Mail User Agent

Program used for reading and writing mail. For example:

Pine , Netscape, Eudora

Mailbox access methods used by MUAs:

POP , IMAP

MTA: Mail Transport Agent

Program used for transporting mail from one host to another like:

Sendmail, Exchange, qmail, Exim, Postfix

Protocol between MTAs: SMTP

MDA: Mail Delivery Agent

MDA delivers the mail to the users mailbox

MUA MTA MDA communication


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Scenario1: When the sender and the receiver of an email are on the same system, we needonly two user agents.

Scenario 2: When the sender and the receiver of an email are on different systems, we need two

UAs and a pair of MTAs (client and server)

Scenario 3:When the sender is connected to the mail server via a LAN or a WAN, we

need two UAs and two pairs of MTAs (client and server).


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Scenario 4:

Push Vs Pull


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When both sender and receiver are connected to the mail server via a LAN or a WAN, we

need two UAs, two pairs of MTAs (client and server), and a pair of MAAs (client and server).

This is the most common situation today.

The user agent (UA) provides service to the user to make the process of sending and receiving

a message easier.

Some examples of command-driven user agents are mail, pine, and elm

Hypertext Transfer Protocol (HTTP)

i. HTTP is the protocol used to access resources on the World Wide Webii. A browser application is used to send a request to the WWW server for a resource, e.g. a

web page, graphics file, audio file, etc.iii. The server responds by sending the resource (a file) to the client and closing the connection

Benefits of E-Mail

Inexpensive communications medium

Generates additional revenue opportunities

Builds relationships

Results are measurable

Quick response cycles

Drives web-site traffic

Popular Medium - 45% US population 119 million

Complements other communication channels

Cost Savings due to E-Mail Usageamong U.S. Companies

Newsgroups

protocol

NNTP (Network News

Transfer Protocol)

client

Email client Newsgroups: Protocol

NNTP

newsgroups stored on

NNTP news servers

server usually providedby ISP

should carry a widerange of newsgroups

public servers carry

limited ranges of

newsgroups

port 119

Newsgroups: Quality of

Service

communication

bandwidth

news servers

client application usually an email

client also


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File Transfer Protocol (FTP)

Protocol for copying files between client and an FTP server

Uses a TCP connection for reliable transfer of files with error-checking

Most browsers support FTP, or you can use a dedicated FTP client program, e.g WS_FTP

Trivial File Transfer Protocol (TFTP) is a lightweight version for small memory devices

Telnet Telnet allows a user to run commands and programs remotely on another computer

across the Internet

The user runs a Telnet client program on the local host

A Telnet server process must be running on the remote host

The user must have the necessary permissions and password to access the remote host

Some Port Assignments

21 FTP 25 smtp (mail) 79 finger

23 Telnet 70 gopher 80 HTTP

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