In last article we have discussed what is a firewall. Let us discuss now proxy servers in detail.

Proxy servers are also commonly used in firewalls. A proxy server is server software that runs on a host in a firewall, such as a bastion host. Because only a single proxy server (instead on the many individual computers on the network) interacts with the Internet, security can be maintained. That single server can be kept more secure than hundreds of individual computers on a network.

When some one from the Intranet wants to access a server on the Internet, a request from the computer is sent to the proxy server. The proxy server contacts the server on the Internet and then the proxy server sends the information from the internet server to the computer inside the corporate network. By acting as a go-between, proxy servers can maintain security as well as log all traffic between the Internet and the network.

How Proxy Servers Work

• System administrator can set up these proxy servers to be used for many services. System administrator decides which Internet services must go through a proxy server. Specific proxy server software is required for particular Internet service.
• When a computer from Intranet makes a request to the Internet - such as to get a web page from a web server - it looks to that computer as if it connects directly to the web server on the Internet. In fact, the internal computer from Intranet contacts the proxy server with its request, which in turn contacts the Internet server. The Internet server sends the web page to the proxy server, which then forwards the pages to the internal computer.
• Proxy servers can also be used as a way to log the Internet traffic. 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 against the network.
• Proxy servers can implement some other security schemes as well. It can put up lots of restrictions whether files can be received or sent etc.
• Proxy servers can also be used to speed up performance of some internet services by cashing data. I.e. keeping copies of the requested data. E.g. a web proxy server could cache many web pages. E.g. if one person requests a page which is already existing in cashe, then internal computer gets that page from proxy server directly leading to a fairly high speed connection rather than connecting at a lower speed to internet.

There are many proxy servers available in the market. The most commonly used in pune especially in the net cafes is Ms Proxy Server. Let us understand the features of proxy server keeping Ms Proxy Server as an example.

Array-based content caching
New! Proxy Server now allows you to set up distributed caching among multiple Proxy Server computers. Arrays allow a group of Proxy Server computers to be treated and administered as a single, logical entity. Arrays provide load balancing, fault tolerance, scalability, and ease of administration.

Hierarchical content caching
New! Proxy Server now enables caching across a hierarchical connection of individual Proxy Server computers or arrays, enabling distributed deployment to branch offices and departments. Requests from clients are sent upstream through the hierarchy until the requested object is found.

Cache array routing protocol
New! This is a new approach for performing scalable array-based and hierarchical-based caching that has been submitted to the IETF. The new protocol, developed by Microsoft, provides substantial advantages over alternative approaches in performance to enable linear scalability with cache arrays or hierarchies. Microsoft Proxy Server 2.0 is the first product to make use of this protocol.

Active Intelligent Caching
Microsoft Proxy Server 2.0 automatically determines which Web sites are most used and how frequently their content is refreshed. Proxy Server uses this information to proactively preload that Web content into its cache during periods of low network use. This provides a consistent, accelerated Internet experience for all users accessing these Web sites, without requiring network manager intervention.

FTP and HTTP cache support
New! Now you can cache not only HTTP 1.0 objects-you can also cache HTTP 1.1 and FTP objects. There is greater control over the Time-to-Live (TTL) setting as well, with Microsoft Proxy Server version 2.0.

Hypertext Transfer Protocol (HTTP) version 1.1
New! Implementation of HTTP 1.1 allows Proxy Server to use persistent client-to-proxy server connections, persistent proxy server-to-Internet server connections, read-range, and virtual hosts. Full support of HTTP 1.1 helps Microsoft Proxy Server deliver significant performance gains. (NOTE: Full HTTP 1.1 support requires use of the Internet Information Server 4.0 HTTP engine, which is not supported in the initial beta.)

Improved cache and Proxy performance
New! Microsoft Proxy Server 2.0 offers unbeaten performance to meet real-world requirements of fulfilling requests not only from the cache but also from across a live Internet connection-all while performing the full range of security and managed access. Microsoft Proxy Server 2.0 is up to 40 percent faster than Proxy Server 1.0.

Easy, comprehensive management support

Windows NT Server integration
Microsoft Proxy Server capitalizes on features that make Windows NT® Server a secure, scalable network operating system. This includes the best integration with the Windows NT Server directory service for easier manageability and reduced total cost of ownership. Microsoft Proxy Server supports a single user logon for network services and applications so user accounts do not have to be recreated for Proxy Server.

User access control
Network managers can use Microsoft Proxy Server to set detailed user and group permission lists by Internet protocol in the Web Proxy, WinSock Proxy, and SOCKS Proxy components.

Site filtering
Network managers can specify a list of Internet addresses (IP addresses, IP address ranges, or URLs) to be exclusively permitted or denied for access by users behind the Proxy Server.

GUI-based administration
Microsoft Proxy Server's Internet Service Manager provides an easy-to-understand way to administer a local or remote proxy server computer, proxy array, or proxy hierarchy.

Web administration
New! You can administer Microsoft Proxy Server locally or remotely via a Web browser for added management flexibility and ease-of-use. You can even create customized HTML error pages. (note: Web Administration Tool is currently available as a separate download.)

Command line administration
New! This tool lets you manage Microsoft Proxy Server through MS-DOS® operating system prompts if that is your preference. You can configure and manage one or more local or remote servers with this tool.

Array administration
New! Multiple proxy servers can be administered simultaneously via transparent array-based administration. This allows a change to be propagated to other proxy servers with a single mouse click.

Configuration backup & restore
New! You can now back up your server configuration to a file or roll back to a previous configuration.

Client auto-configuration
New! You can automatically configure Web Proxy clients by using predefined JavaScripts or by creating your own scripts for great ease-of-use and fast enterprise-wide deployment. You can also use the Internet Explorer Administration Kit or Microsoft Systems Management Server to automate the proxy client installation.