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A proxy server shares one internet connection with ALL the computers on your local network or it is a computer that

offers a computer network service to allow clients to make indirect network connections to other network services. So

basically a proxy (proxy server) is a server that acts as mediator between the client (the computer of a user) and

server (the computer on the other ends of network connection on which the information requested by the user

appears for example web server site.) When clients request data from an Internet resource,traffic goes from your web

browser/application first through the proxy before it reaches the requested sources and back through the proxy then

the proxy will transmit the data to you.

A proxy server sits between a client application, such as a Web browser, and a real server. It intercepts all requests

to the real server to see if it can fulfill the requests itself. If not, it forwards the request to the real server.

Do not confuse a proxy server with a NAT (Network Address Translation). Although they appear to be very similar, a

proxy server actually does the work of connecting to, responding to, and receiving traffic from the Internet. In other

words, it acts on behalf of the client computer. A NAT, on the other hand, merely changes the origination address of

traffic coming through it and passes it to the Internet. The computer behind the NAT,not the NAT itself, does the work.

The NAT is intended to be transparent to the whole process.

For those who understand the OSI (Open System Interconnection) model of networking,the technical difference

between a proxy and a NAT is that the proxy server works on the transport layer (layer 4), or higher of the OSI model,

whereas a NAT works on the network layer (layer 3).

How Proxy Servers Work :

1. When a computer on the intranet makes a request out to the Internet-such as to retrieve a Web page from a Web

server-the internal computer actually contacts the proxy server, which in turn contacts the Internet server. The

Internet server sends the Web page to the proxy server, which then forwards the page to the computer on the

intranet.

2. Proxy servers log all traffic between the Internet and the intranet. For example, a Telnet proxy server could track

every single keystroke hit in every Telnet session on the intranet-and could also track how the external server on the

Internet reacts to those keystrokes. Proxy servers can log every IP address, date and time of access, URL, number of

bytes downloaded, and so on. This information can be used to analyze any attacks launched against the network. It

can also help intranet administrators build better access and services for employees.

3. Some proxy servers must work with special proxy clients. A more popular approach is to use off-the-shelf clients

such as Netscape with proxy servers. When such an off-the-shelf package is used, it must be specially configured to

work with proxy servers from a configuration menu. Then the intranet employee uses the client software as usual.

The client software knows to go out to a proxy server to get the data, instead of to the Internet.

4. Proxy servers can do more than relay requests back and forth between an intranet and the Internet. They can also

implement security schemes. For example, an FTP proxy server could be set up to allow files to be sent from the

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Internet to a computer on the intranet,but to block files from being sent from the corporate network out to the Internet-

or vice versa. In this way, intranet administrators can block anyone outside the corporation from downloading vital

corporate data. Or they can stop intranet users from downloading files which may contain viruses.

5. Proxy servers can also be used to speed up the performance of some Internet services by caching data-keeping

copies of the requested data. For example, a Web proxy server could cache many Web pages, so that whenever

someone from the intranet wanted to get one of those Web pages, they could get it directly from the proxy server

across high-speed intranet lines,instead of having to go out across the Internet and get the page at a lower speed

from Internet lines.

The different types of Proxy Servers :

There are many different types of Proxy Servers out there. Depending on the purpose you can get Proxy Servers to

route any of these common protocols, and many more ;

1)FTP Proxy Server:

Relays and caches FTP Traffic.

2)HTTP Proxy Server:

http://www.eukhost.com/reseller-hosting.php

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A one way request to retrieve Web Pages.

3)Socks Proxy Server:

A newer protocol to allow relaying of far more different types of data, whether TCP or UDP.

4)NAT Proxy Server:

This one works a little different, it allows the redirection of all packets without a Program having to support a Proxy

Server.

5)SSL Proxy Server:

An extension was created to the HTTP Proxy Server which allows relaying of TCP data similar to a Socks Proxy

Server. This one done mainly to allow encryption of Web Page

requests.

Furthermore, a Proxy Server can be split into another two Categories:

1)Anonymous:

An Anonymous Proxy Server blocks the remote Computer from knowing the identity of the

Computer using the Proxy Server to make requests.

2)Transparent:

A Transparent Proxy Server tells the remote Computer the IP Address of your Computer.

This provides no privacy.

Anonymous Proxy Servers can further be broken down into two more categories, Elite and Disguised. An Elite Proxy

Server is not identifiable to the remote computer as a Proxy in any way. A Disguised Proxy Server gives the remote

computer enough information to let it know that it is a Proxy, however it still does not give away the IP of the

Computer it is relaying information for.

2;

How the proxy server works

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Once you have configured your web browser as described, your browser will load a CGI script each time it isrestarted. This script redefines the function that determines how to fetch the URL that is being requested. If the URLmatches a pattern or a site that requires a proxy, it will connect to the proxy server rather than going directly to thesite.

(USR = User on IBM.Net or another ISP; PXY = BOL web proxy server; SRV = web server restricted to UCLA)

Step 1: User starts browser, connects to proxy server to get the Proxy

Automatic Configuration (PAC) file.

fetch request: proxy.ucla.edu/cgi/proxy

+-----+ +-----+

| U | | P |

| S | ==================>| X |

| R | | Y |

+-----+ +-----+

Step 2: Proxy server returns "proxy", which configuresbrowser to do proxying.

+-----+ +-----+

| U | "proxy" loaded | P |

| S || X | | R |

| R | | Y | | V |

+-----+ +-----+ +-----+

Step 4b2: Proxy contacts server and requests page.

+-----+ +-----+ +-----+

| U | | P | request URL | S |

| S | | X | ==================>| R |

| R | | Y | | V |

+-----+ +-----+ +-----+

Step 4b3: Server sees request from ucla.edu domain (proxy address)

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and returns URL to proxy.

+-----+ +-----+ +-----+

| U | | P | return URL | S |

| S | | X |

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Analogy: Just imagine the postman is the proxy server. You can either choose to deliver the mail to your friend via the

postman or drive your own self to your friend house. Ironically, the postman might save you from any accident, and

perhaps your friend wont know who the sender is. Most importantly, police would not stop the postman.

Picture tells thousand words

Connection with proxy server:

Normal connection without proxy server:

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5 reasons why you should use proxy server?

Bypassing

We all believe internet is a continent of freedom, and it should be freed from the pollution of government policy, and

the most retarded company filtering. With proxy server, you can unblock the web filter and access to your favorite site

without any restriction.

Anonymity

Every time you connect to internet, your computer will generate a unique IP number which will reveal your private

information to others. This information could be your location, internet service provider and your browsing habits.

Using a proxy server allows you to surf the Internet or use Internet-based software totally anonymous to keep off

them effectively.

Speed Booster

A proxy server would store a cached copy of a particular website you visit for the first time. Hence, the second time

you revisit to the same website, the proxy server can call up its cached copy instead of having to send another

request to the main server. This speeds up data transmission and also reduces server load.

Lesser Bandwidth

As described above, the proxy server will deliver a cached copy of the website to you instead of using bandwidth to

retrieve the website from the hosted server. This is especially useful for the users who have the limited amount of

bandwidth provided by the ISP.

Security

Proxy Server acts as a security guard to protect you from the unexpectedly malware and virus attack. In other words,

proxy servers can filter out malicious content in websites easily to prevent browse-by malware infections.

In addition, most of the good proxy server will enhance your security by providing you the Secure Sockets Layer

(SSL). SSL or sometimes called HTTPs proxy is the extra layer of security that encrypts all the coming in and going

out information to prevent unauthorized access. This makes the connection between the user and the remote server

more secure.

How does Proxy Server works

Introduction

A Proxy Server is a computer that offers network and internet access services to the clientcomputers in a network. A proxy is a stand-in for you - someone who does something on

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your behalf. A proxy server is a kind of stand in for your computer. In an enterprise that

uses the Internet, a proxy server is a server that acts as an intermediary between a

workstation user and the Internet so that the enterprise can ensure security, administrativecontrol, and caching service.

By using the proxy server you can hide, conceal and make your network id anonymous by

hiding your IP address. A proxy server is associated with or part of a gateway server that

separates the enterprise network from the outside network and a firewall server thatprotects the enterprise network from outside intrusion. In short, a Proxy Server can bedescribed as 'A server that sits between a client application, such as a Web

browser, and a real server.' To get the anonymous status on the network or Internet,strong intermediate methods are employed like cryptography etc.

How does Proxy Server works?

A proxy server receives a request for an Internet service (such as a Web page request) from

a user. If it passes filtering requirements, the proxy server, assuming it is also a cacheserver , looks in its local cache of previously downloaded Web pages. If it finds the page, it

returns it to the user without needing to forward the request to the Internet. If the page isnot in the cache, the proxy server, acting as a client on behalf of the user, uses one of itsown IP addresses to request the page from the server out on the Internet. When the page isreturned, the proxy server relates it to the original request and forwards it on to the user. A

good example, and the one you probably see the most, is a web proxy. When configured touse a proxy, your web browser contacts the proxy server for each web access instead ofgoing directly to the target server on the internet. The proxy server then turns around and

makes the "real" request of the web server. The proxy server gets the response, and then

passes it back to you.

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There is a large number of the software available that allows you to hide your IP address

with the help of the proxy servers. The well known software for this purpose is Hide IP,Stealth surf, Netconceal, Anonymous surfing, Proxify and Ghost surf. To the user, the proxy

server is invisible; all Internet requests and returned responses appear to be directly withthe addressed Internet server. (The proxy is not quite invisible; its IP address has to be

specified as a configuration option to the browser or other protocol program.)__________________

Types of Proxy Servers

Many different types of Proxy Servers are available. Some common types are-1. FTP

2. HTTP3. Gopher4. IRC

5. MSN6. AIM7. ICQ

8. VOIP

9. SSL

Depending on the purpose you can get Proxy Servers to route any of these commonprotocols, and many more. So out of the common types of Proxy Servers, you end up withthe following:

FTP Proxy Server:

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Relays and caches FTP Traffic.

HTTP Proxy Server:

A one way request to retrieve Web Pages.

Socks Proxy Server:

A newer protocol to allow relaying of far more different types of data, whether TCP or

UDP.

NAT Proxy Server:

This one works a little different, it allows the redirection of all packets without a

Program having to support a Proxy Server.

SSL Proxy Server:

An extension was created to the HTTP Proxy Server which allows relaying of TCP

data similar to a Socks Proxy Server. This one done mainly to allow encryption ofWeb Page requests.

Furthermore, a Proxy Server can be split into another two Categories:

Anonymous

An Anonymous Proxy Server blocks the remote Computer from knowing the identity

of the Computer using the Proxy Server to make requests.

Transparent

A Transparent Proxy Server tells the remote Computer the IP Address of yourComputer. This provides no privacy.

Anonymous Proxy Servers can further be broken down into two more categories, Elite and

Disguised. An Elite Proxy Server is not identifiable to the remote computer as a Proxy in any

way. A Disguised Proxy Server gives the remote computer enough information to let it knowthat it is a Proxy, however it still does not give away the IP of the Computer it is relaying

information for.

How to Setup a Proxy Server

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A proxy server is one that receives requests intended for another server and that acts on the behalf of

the client (as the client proxy) to obtain the requested service. It is often used when the client and the

server are incompatible for direct connection. For example, the client may be unable to meet the

security authentication requirements of the server but may be required to access some services. It

may also be used for screening purposes to enable the administrator to control access to undesirable

sites. The proxy server may also be used for caching purposes, which enables faster access to

frequently used websites. All the computers connected to the LAN access the Internet through a singleIP address, resulting in improved security simply because the number of ports exposed is reduced.

Proxy servers work on the seventh layer (theApplication Layer) of theOSI model, thus tending to be

application dependent unlikefirewallsthat work at lower layers. They are also more difficult to install

and maintain than firewalls, as proxy functions for each application protocol like HTTP, SMTP, or

SOCKS must be configured individually. However, a properly configured proxy server improves

network security and performance. Since proxy servers function at the OSI Application layer, their

filtering capabilities are relatively intelligent. For example, proxy web servers can check the URL

(Uniform Resource Locator) of outgoing requests for Web pages by inspecting HTTP, GET and POSTmessages. Using this feature, network administrators can bar access to illegal domains but allow

access to other sites. Ordinary firewalls, in contrast, cannot see Web domain names inside those

messages. Likewise, ordinary routers can filter incoming data traffic byport numberor network

address, but proxy servers can also filter based on application content inside the messages.

WinProxy

One of the most popular proxy servers available for Windows based systems isWinProxy. One of the

reasons for its popularity is that no software has to be installed on the client systems. This is possible

since WinProxy is a transparent proxy server, meaning that it also provides NAT (Network Address

Translation). Due to this, the client system is virtually unaware of the proxy servers existence. Apart

from the usual caching and security features, it also supports important protocols like HTTP, Real

Audio/Video, Mail,FTP,NNTPNews, Telnet, Socks, Secure Sockets,DNS, IMAP 4, etc.

The WinProxy Server may be installed and configured as follows:

1. Install the TCP/IP protocol on all systems connected to the network.

2. Run the Install Wizard. The first screen is the product registration screen, which requires the

user to enter the product key.

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3. The next two screens require information about the Internet connection. Select the

connections type and name.

4. Enter the username and password of the Internet connection to be used.

5. WinProxy then configures the internal and external IP addresses. It automatically assigns a

unique address to each device on the LAN as internal addresses. The IP address that the ISP

assigns to the modem/router is taken as the external address.6. WinProxy then prompts the user to disconnect from the Internet if he/she is already

connected.

7. In the final step, WinProxy works through all the steps and verifies that all operations have

been performed properly.

What is a proxy server?

A proxy server, also known as a "proxy" or "application level gateway", is a computerthat acts as a gateway between a local network (e.g., all the computers at one companyor in one building) and a larger-scale network such as the Internet. Proxy serversprovide increased performance and security. In some cases, they monitor employees'use of outside resources.

A proxy server works by intercepting connections between sender and receiver. Allincoming data enters through one port and is forwarded to the rest of the network viaanother port. By blocking direct access between two networks, proxy servers make itmuch more difficult for hackers to get internal addresses and details of a privatenetwork.

Some proxy servers are a group of applications or servers that block common Internetservices. For example, an HTTP proxy intercepts web access, and an SMTP proxyintercepts email. A proxy server uses a network addressing scheme to present oneorganization-wide IP address to the Internet. The server funnels all user requests to theInternet and returns responses to the appropriate users. In addition to restricting accessfrom outside, this mechanism can prevent inside users from reaching specific Internetresources (e.g., certain web sites). A proxy server can also be one of the components ofa firewall.

Proxies may also cache web pages. Each time an internal user requests a URL from

outside, a temporary copy is stored locally. The next time an internal user requests thesame URL, the proxy can serve the local copy instead of retrieving the original acrossthe network, improving performance.

Note: Do not confuse a proxy server with a NAT (Network Address Translation) device.A proxy server connects to, responds to, and receives traffic from the Internet, acting onbehalf of the client computer, while a NAT device transparently changes the originationaddress of traffic coming through it before passing it to the Internet.

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For those who understand the OSI (Open System Interconnection) model of networking,the technical difference between a proxy and a NAT is that the proxy server works onthe transport layer (layer 4) or higher of the OSI model, whereas a NAT works on thenetwork layer (layer 3).