Port forwarding issue

hi guys

i have a simple question !

i have two ips . a valid and internal(172.16.11.2)
i want to use port forwarding to forward any request to valid IP port 8001 to internal ip port 80 .

i use this rule :

sysctl -w net.ipv4.ip_forward=1 
iptables -t nat -A PREROUTING -p tcp --dport 8001 -j DNAT --to-destination 172.16.11.2:80
 iptables -t nat -A POSTROUTING -p tcp --dport 80 -j MASQUERADE 

there is a problem !

sometime on my apache server http changes to https in some pages ! in this situation redirection does not work !and https page wont load !
how can i fix that !!

or is there any way to forward port to a ip address ??

for example : any request to port 8001 redirect to a ip address ???

Configure two external ports to be mapped internally to the HTTP and HTTPS ports. Use the external SSL port in your redirects. It depends on how the web application is configured. See also Apache mod_rewrite