Web Proxy ServerWeb Proxy Server

Anagh Pathak

Jesus Cervantes

Henry Tjhen

Luis Luna

What is a Web Proxy Server?What is a Web Proxy Server?

It is a specialized HTTP Server.Functions as a firewall.

– Protects client computers from Hackers by limiting outside access to clients.

Allows all clients connected to Web Proxy Server to access Internet from behind “firewall.”

Client computer(s) are allowed access past firewall with minimum effort and without compromising security.

How Does A Web Proxy How Does A Web Proxy Server Work?Server Work?

Web Proxy Server listens for any request from clients.

All requests are forwarded to remote internet servers outside firewall.

Also listens for responses or request from outside the firewall (external servers) and sends to them to internal client computers.

Usually, all clients with a subnet use the same proxy server.

This makes it possible for the proxy server to cache documents that are requested by one or more clients (repeatedly).

For clients using a web proxy server, it is as if they are getting responses directly from a remote server.

Clients without a Domain Name Service can still access the Web

All that is needed is the proxy server’s IP address. Most Web Proxy Servers are implemented on a

per-access method basis.– It can allow or deny internet requests according to the

protocol used.– For Example: A proxy server can allow calls to FTP

while but deny calls to HTTP servers.

How Do Web Browsers How Do Web Browsers Access the Internet?Access the Internet?

In some cases, certain browsers cannot access the Web because they are behind a firewall.

In these cases, the web proxy server can retrieve any desired files for them.

Caching Documents?Caching Documents?

Caching documents means keeping a copy of internet documents so the server doesn’t need to request them over again.

It is more effective with the web proxy server than for the client.– Saves disk space because only one copy needs to be

cached. System administrator can also predict which

documents are worth caching and which ones are not.

Benefits of Caching With A Benefits of Caching With A Web Proxy Server?Web Proxy Server?

Reduces the load on the server itself. Allows server to get information from the cache

when responding to repeated client requests for the same document or data.

Also makes it possible to browse the Web even if the Web Proxy Server or external network is down (as long as clients can connect to proxy server).

Controlling Access to the Controlling Access to the Internet and Subnets?Internet and Subnets?

Web proxy server makes it possible to filter client “transactions” at the protocol level.

Controls access to services for individual methods, hosts, as well as domains.

For Example, web proxy servers allows administrators to:– Decide which requests to grant permission to and which ones to turn

down.– Specify the URL(s) masks of locations that you don’t want the

proxy server to serve.– Specify which protocols clients can use the services based on their

IP address.

Configuring Browsers to Use a Configuring Browsers to Use a Proxy Server?Proxy Server?

In order to use a web proxy server, the proxy server must channel a browsers request.

Most browsers allow users to configure them so they send their requests directly to a proxy server.

For certain browsers, users can ID a proxy server by identifying the server’s domain name or IP address.

Browsers will not send their request to a proxy server unless users configure their browser to look for the proxy server.

Proxy Server ExamplesProxy Server Examples A caching web proxy is a simple example of an

HTTP intermediary

An Ordinary Web Transaction Via An Ordinary Web Transaction Via ServerServer

When the user enters:– http://mycompany.com/information/ProxyDetails.html

The browser converts it to:– Get / information/ProxyDetails.html

Communicating Via Proxy ServerCommunicating Via Proxy Server

The Proxy server acts as both a server system and a client system.

The proxy server uses the header fields passed to it by the browser without modification when it connects to the remote server.

A complete proxy server should be able to communicate all the Web protocols, the most important ones being HTTP, FTP, Gopher, and WAIS.

When a browser sends a request through a proxy server, the browser always uses HTTP for the transactions with the proxy server.

HTTP Browser Request to Remote HTTP HTTP Browser Request to Remote HTTP TransactionTransaction

When you use a proxy server as client system, it acts as a browser to receive documents.

When you enter the this URL– http://mycompany.com/information/ProxyDetails.html

The browser converts the URL to:– GET http://mycompany.com/information/ProxyDetails.html

The proxy server converts this request to:– GET /information/ProxyDetails.html

HTTP Browser Request to Remote HTTP HTTP Browser Request to Remote HTTP TransactionTransaction

An HTTP transaction via a proxy server

HTTP Browser Request to Remote FTP HTTP Browser Request to Remote FTP TransactionTransaction

An FTP transaction via a proxy server

Proxy CachingProxy Caching

Proxy server stores all the data it receives as a result of placing requests for information on the Internet in it’s cache.

Cache simply means memory.The cache is typically hard disk space, but it

could be RAM.

Advantages of Caching Advantages of Caching DocumentsDocuments

Save users considerable time when they requested documents normally located out on the Internet.

Save considerable network cost and connection time. Reduce the amount of disk space browsers use because

many local browsers can use a single copy of a cached document.

Caching is disk based; when you restart the server, documents that you cache are still available.

Caching a Document on a Caching a Document on a Proxy ServerProxy Server

Scenario 1:- user A request a web page

(using Netscape for example)- the request goes to the proxy

server- the proxy server checks to see

if the document is stored in cache

- the document is not in cache so the request is sent to the Internet

- the proxy server receives the request, stores (or caches) the page

- the page is sent to user A where is is viewed

Retrieving Cached DocumentsRetrieving Cached Documents

Scenario 2:- user B request the same page as

user A (ie. resource.com)- the request goes to the proxy

server- the proxy server checks its

cache for the page- the page is stored in cache- the proxy server sends the page

to user B where it is viewed- no connection to the Internet is

required

Managing Cached DocumentsManaging Cached Documents

Many documents available on the Internet are “living” documents.

Determining when documents should be updated or deleted can be difficult task.– Some documents can remain stable for a very long time

and then suddenly change.– Other documents can change weekly or a daily basis.

You need to decide carefully how often to refresh or delete the documents held in cache.

Access ControlAccess Control

Proxy Server has the ability to control access to resources since it sits between a network’s users and the Internet.

When configured in this way, a proxy server provides institutions with an effective tool to provide access to remote users.

How Proxy Access Control How Proxy Access Control works:works:

Scenario: an off-site (or off-campus) user connects to the Internet via an ISP and wants to connect to an IP-restricted resource:

- user Y from outside internal network requests access to internal resource- proxy server prompts user Y for validation

- user Y is validated (proxy server masks user Y's IP-address)

- resource.com assumes user Y is an institutional computer

For More Information, VisitFor More Information, Visit

Http://libmain.stfx.ca/gbertran/proxy2.htm Http://vms.process.com/~help/helpproxy.html