the public DNS server (usually your domain registrar) needs to point to a publically accessible IP address for your openifre server. Typically this would point at a static public IP address at your office or whatever, and then you would have NAT setup to forward/translate those public requests to your openfire server. You will need to NAT the ports needed by Openfire such as 9090, 5222, etc. You can login to you openfire admin page and see which ports it would like to use, then based on your judgement, NAT/open those ports.