I’m not sure what OS you’re working from, but the following is a high-leve for windows server enviroments.
1. Publish the Intranet via IIS. (If it’s accessable within the nexwork, then this is already done.)
2. Next you’ll need a public IP address. Contact your ISP if you don’t have one spare.
3. Have your front-end firewall translate (NAT)from the public IP address to the local IP address.