Using Apache Proxy to Suppress Banner Ads

No matter how much you have, Internet bandwidth never seems to be enough. At home, I dial up on an oldish analog exchange to the Internet, rarely getting connections better than 4800 bps; at the office, I have a (shared) 64KB leased line to our U.S. office and thence to the Internet. However, no matter where I surf (it's part of my job), I have always wished there were a way to avoid waiting for pages to display while loading banner ad graphics from the remote server.

I am running an old, completely hacked version of Red Hat (2.0 to be precise) with kernel 2.2.10 on my 66MHz 486 PC at home. I use this system for browsing (mainly using Lynx), software development and fooling around with Linux. My wife and two children also use it, primarily for browsing and e-mail using one of the web-based e-mail services with Netscape Communicator.

Since I first installed Linux on this system a few years ago, I've been running the Apache web server to serve local content. More recently, I've also enabled Apache's caching Proxy module to maintain a local cache of commonly accessed documents, speeding up Internet access somewhat. The version of Apache I'm running is 1.3.3 (yes, I should upgrade to the latest and greatest, but there's no pressing hurry).

The Apache web server (http://www.apache.org/) is a well-known HTTP server and is part of most, if not all, Linux distributions. Along with being the world's most popular web server, running on over 56% of web sites (Netcraft survey at http://www.netcraft.com/), Apache also has features which helped me replace graphics from well-known banner ad sites with an innocuous local graphic.

Since the distribution I'm running is so old, I will describe the methodology of replicating this on a more modern distribution, namely Red Hat 6.0. Most other popular distributions of Linux will require the same or similar steps.

In order to use Apache for this purpose, I had to set it up as an HTTP Proxy, using mod_proxy, and enable and use the URL rewriting engine built into Apache (mod_rewrite).

In a nutshell, you must first set up Apache to act as a proxy server for the browsers on your local network (or for a single system, which is what I do at home) and tell the client browsers to use that Apache host as a proxy. Then use the powerful mod_rewrite URL rewriting engine to search for banner ad HTTP requests (these match the URLs of well-known banner ad server hosts) and substitute a local graphic for them. With this done, you can sit back and watch your web pages flow into your browser, while that irritating advertising is automatically replaced with a more soothing and altogether more relevant graphic.

You will need to be root while following the steps discussed here.

The first step is loading and enabling the proxy module (mod_proxy) which is part of Apache. In most distributions, you enable mod_proxy by appending the following line to your Apache server's configuration file (/etc/httpd/conf/httpd.conf or /usr/local/apache/etc/httpd.conf):

ProxyRequests on

To check if the module was loaded okay, restart the web server with the command:

killall -1 httpd

If you get an error message like:

Invalid command 'ProxyRequests', perhaps misspelled or defined
by a module not included in the server configuration

then you need to either locate the Apache Proxy module, or download and install a version of Apache which has mod_proxy available. Installation is outside the scope of this article. See the Apache HOWTO at www.apache.org/docs-1.2/mod/mod_proxy.html.

Once you have the Apache proxy configured and running, you can tell your client browsers to use it. In Netscape Communicator, select Edit/Preferences/Advanced/Proxies and “Manual Proxy Configuration”. Click on the “View” button, and enter the name of the host running Apache in the text entry boxes for “FTP Proxy:” and “HTTP Proxy:”, using 80 as the port number for each.

For Lynx, edit the global Lynx configuration file found by default in /etc/lynx.cfg or /usr/local/lib/lynx.cfg and change these lines

#http_proxy:http://some.server.dom:port/
#http://some.server.dom:port/
#ftp_proxy:http://some.server.dom:port/

to look like:

http_proxy:http://apache.my.dom:80/
http://apache.my.dom:80/
ftp_proxy:http://apache.my.dom:80/