Working configuration for transparent FTP caching proxy with Squid3 and IPTABLES

If I understand you correctly, what you want to do isn't going to be handled simply by configuring iptables. The REDIR target can only be used to target processes running on the local system. I believe attempting to use a DNAT target to forward the to the remote squid box would remove some of the information the remote squid box needs to properly handle the request

If you allow me to guess a bit. I think you are trying to leave the default gateway as 192.168.1.1 on your host and then send your port 80 traffic across the vpn right?

The remote squid needs some configuration so that it can actually act as a transparent proxy. If you can setup the correct iptables redirection on the squid host, and the remote host is in the network path, then it is possible to do use some advanced routing to forward all port 80 requests across the vpn.

P.S. If I am understanding your needs correctly add a comment, I can update my answer with more details about how to setup routing.

If your data is correct, then there ist nothing wrong with squid.

The url you posted is http:// ubuntuforums.org/ - see the space between http:// and ubuntufoums.org/