Firewalls and Proxies Explained

Table of Contents

A Proxy is a central machine on the network that allows other machines in that network to use a shared Internet connection. Proxy servers are intermediate servers which accept requests from clients and forward them to other proxy servers, a source server, or service the request from their own cache. The proxy is also called 'server' or 'gateway'. Proxy allows users on a network to browse the Web, send files over FTP, and work with E-mail and other Internet services.

A Firewall Proxy provides Internet access to other computers on the network but is mostly deployed to provide safety or security. It controls the information going in and out the network. Firewalls are often used to keep the network safe and free of intruders and viruses. Firewall proxy servers filter, cache, log, and control requests coming from a client. A firewall proxy is one that is used for restricting connections from a proxy to the outside world or to the source server inside of the LAN. This is different from a conventional firewall, in that a conventional firewall restricts connections coming from the outside world.

How the Proxy Works

Simply put, proxy are gateway applications used to route Internet and web access from within a firewall. Proxy servers work by opening a socket on the server and allowing the connection to pass through. There is often only one computer in a company with direct Internet connection. Other computers have access to the Internet using that computer as gateway.

A proxy basically does the following:

1. Receives a request from a client inside the firewall
2. Sends this request to the remote server outside of the firewall
3. Reads the response
4. Sends it back to the client

Usually, the same proxy is used by all of the clients on the network. This enables the proxy to efficiently cache documents that are requested by several clients.

SOCKS4 or SOCKS5 Proxy?

In a SOCKS network, all network application data flows through SOCKS, enabling SOCKS to collect, audit, screen, filter and control the network data, and create a network application data warehouse.

It is recommended to use SOCKS5 proxy with PostCast Server. SOCKS4 performed three functions: connection request, proxy server setup and application data relay. SOCKS5 brings authentication to the table. With authentication, SOCKS5 adds two messages. SOCKS5 makes configuring clients easier and includes support for UDP and TCP applications such as SNMP and audio/video applications such as RealAudio. It supports communications among networks with different IP addressing schemes, and supports authentication and encryption.

Tunneling Proxy

Tunneling allows users to perform various Internet tasks despite the restrictions imposed by firewalls. This is made possible by sending data through HTTP (port 80). Additionally, Tunneling protocol is very secure, making it indispensable for both average and business communications. SSL (Secure Sockets Layer) tunneling protocol allows a web proxy server to act as a tunnel for SSL enhanced protocols. The client makes an HTTP Request to the proxy and asks for an SSL tunnel. A Tunneling Proxy operates on port 443.

Proxy Software

1. Microsoft's Internet Connection Sharing
   http://support.microsoft.com/support/kb/articles/Q234/8/15.ASP
2. WinGate 3.0
   http://www.deerfield.com/
3. WinProxy
   http://www.WinProxy.com/
4. NAT32
   http://www.nat32.com/
5. WinRoute
   http://www.winroute.com/
6. Sambar
   http://www.sambar.com/
7. Netproxy
   http://www.grok.co.uk/netproxy/

See Also:

1. Overview
2. Firewalls and Proxies Explained
3. Settings
4. Open Proxy Servers
5. SocksChain Application