Proxy Server

Introduction

• A proxy server services client requests by forwarding :• the requests to the destination server . The requests appear to come from the

proxy server and not from the client.

• the reply from the destination server back to the client. The response is served to the client by the proxy server.

• This technology provides :• a central management point to inspect and filter all incoming and outgoing

traffic

• additional security by isolating the internal clients from the external network.

Introduction

• The main advantages of using a proxy server are:• Hiding internal IP addresses

• Caching HTTP objects, which improves the client application performance

• Access control, which allows more granular control over Internet access

Software

• Linux• Squid

• Windows• Microsoft Proxy Server

• Proxy Server 1.0 (1996)• Proxy Server 2.0 (1997)• Internet Security and Acceleration (ISA) Server 2000 (Windows 2000 Server Only)• Internet Security and Acceleration (ISA) Server 2003 (Windows 2000, 2003 Server Only)• Internet Security and Acceleration (ISA) Server 2006 (Windows 2003 SP1/SP2)• Forefront Threat Management Gateway (Forefront TMG) (2010, Windows Server 2008)

• A Network Router• Firewall• Antivirus program• VPN Server• Web Caching

Function of a Proxy Server

• A proxy server offers four main functions:• Forward proxy

• Reverse proxy

• Proxy chaining

• Caching

Forward Proxy

• Allows client computers in protected networks to connect to the Internet by • Intercepting their requests and forwarding them to the destination server

• Relaying the reply back to the client

Reverse Proxy

• A reverse proxy server passes the request from the Internet to an internal network resource

• The most common form of reverse proxy is publishing Web services to the Internet.

• A proxy server can redirect or deny the request based on the policy rule created by the administrator.

Proxy Chaining

• A proxy server makes use of one or more proxy servers to handle proxy requests.

Caching

• One of the most important functions of Proxy Server

• A proxy server can cache requests from Internet users trying to access published Web servers as well as cache requests from internal users trying to access content from the Internet

• This provides a faster browsing experience to the clients as well as saving important network bandwidth.

Caching Process

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Type of Caching

Type of Caching (cont.)

• Forward Caching• You can use forward caching to provide internal clients with access to

Web objects on the Internet. The ISA Server computer maintains a centralized cache of frequently requested Web objects that can be accessed by any Web browser.

• Objects served from the cache require significantly less processing than objects served from the Internet.

1. Support internal client access the web sites on the internet

2. Maintain a centralized cache of frequently requested web sites

3. Purpose : enhance internal network performance

Type of Caching (cont.)

• Reverse Caching• You can use reverse caching to provide external clients with access

to Web objects from an internal Web server. • The ISA Server computer, which is located in front of the Web server,

forwards requests to the internal Web server only when it cannot retrieve a requested object from its cache.

• ISA Server improves the speed at which external clients receive Web objects.

Type of Caching (cont.)

• Distributed Caching• You set up an array of ISA Server computers to perform distributed

caching.• An array is a group of ISA Server computers that that you manage as a

single, logical entity. • Distributing cached objects enhances caching performance through

load balancing and provides fault tolerance if an ISA Server computer is unavailable.

• You can distribute both forward caching and reverse caching.

Caching Function