Application Layer Firewall?

[darookee]

Hi Everybody!

I'm looking for a way to check incoming connections to my server on the application layer. I know that my ISP uses the Sidewinder G2, which has a thing like this working. It looks into the content of FTP commands and HTTP request to the server and drops them, if they could cause harm.

Is there a software-way? I thought about using squid for as http-proxy configured that it would accept connections from anywhere and then routes it to a local-port where apache listens on... But I don't think that this would work :(

I tried http_filter but that was not like I want this to be...