It took me a while to find this – I needed it for testing purposes, nothing malicious. If you’d like your web server somewhere on the web to pretend to be any other web server, even a secure one, you can do the following. x.x.x.x is your own server and y.y.y.y is the ip of the server you’re trying to mirror. I’m also assuming you only have one network card in the machine and it’s called eth0. The following will mirror a secure web server. If you’d like to mirror a regular web server, replace 443 with port 80.

iptables -t nat -A PREROUTING -p tcp -i eth0 -d x.x.x.x --dport 443 -j DNAT --to y.y.y.y
iptables -t nat -A POSTROUTING -p tcp -o eth0 -d y.y.y.y --dport 443 -j MASQUERADE

If this doesn’t work you probably have to enable packet forwarding like this:

echo 1 > /proc/sys/net/ipv4/ip_forward