Iptables NAT

iptables -t nat -A PREROUTING -i eth0 -d PUBLIC_v4 -p tcp --dport 443 -j DNAT --to INTERN_v4:443

persistant in /etc/network/interfaces:

auto eth0
iface eth0 inet static
  address PUBLIC_v4
  post-up iptables -t nat -A PREROUTING -i eth0 -d PUBLIC_v4 -p tcp --dport 443 -j DNAT --to INTERN_v4:443
  post-down iptables -t nat -D PREROUTING -i eth0 -d PUBLIC_v4 -p tcp --dport 443 -j DNAT --to INTERN_v4:443