F-SECURE INTERNET GATEKEEPER WINDOWS 2000-2003 SERVER 6.61 Administrator's Manual page 321

APPENDIX F 321
Advanced Deployment Options
want to configure a transparent proxy if you want all clients to use the
proxy server without any changes in web browser configurations and if
you want to make sure that all clients use the proxy server.
One method that you can use to configure a transparent proxy is to
modify the network so that all HTTP requests that come from the clients
are silently captured and forwarded to F-Secure Internet Gatekeeper. For
example, you can use a firewall that resides between the clients and the
web servers that they try to access.
Figure F-1 F-Secure Anti-Virus for Internet Gateways deployed with a transparent
proxy
Using a transparent proxy is the best way to provide a reliable and easy
HTTP scanning service with F-Secure Internet Gatekeeper. However,
configuring a transparent proxy may require some modifications in the
network infrastructure. As the traffic has to be captured at the TCP/IP
protocol level, the transparency is achieved in the firewall. It recognizes
and redirects HTTP requests that come from the clients to F-Secure
Internet Gatekeeper.
This way, web browsers do not have to be configured manually and if the
firewall rules are configured properly, filtering policies cannot be
bypassed. As the firewall forwards all HTTP requests silently to F-Secure
Internet Gatekeeper, clients are not even aware that the traffic is being
redirected.
Configuring a transparent proxy can be very easy, depending on the
network infrastructure and the firewall in the network.