Networking Terms and Routing Issues

This page describes networking terms and routing issues that may exist to prevent users accessing your server from the public Internet.

The main issue concerns if your computer publicly available on the Internet. If you have a very simple network and your computer is directly connected (perhaps via a cable or ADSL modem) then it probably is. If you are part of a large organisation then this program may be running on a public host or you may have experts available who can open firewalls and redirect ports to make your computer publicly available. This note and the automated Routing Wizard and associated settings it describes is mostly concerned with the most likely middle case: you are on a small business or home network and there is a Network Address Translation (NAT) router between you and the Internet.

NAT routers allow many hosts "inside" the NAT to share a single public IP address by translating the private address and port used for a connection to the public IP address and a public port. Thus, from the "outside", all connections made by hosts on the private network appear to be coming from one host - whose IP address is the public one assigned by your ISP to the router. This is a terrific way to conserve IP addresses but introduces a problem: how can a client "outside" make a connection to a particular host "inside" if the NAT effectively hides all those hosts behind one IP address?

Most NAT routers can be configured to redirect a particular public port to a port on a particular host inside the private network. Where a router supports Universal Plug and Play (UPnP), the Routing Wizard can automatically set-up this port redirect and determine the public IP address. If UPnP is not supported, then the router will have to be manually configured - see here for details.

Regardless of whether your server is connected directly or via a NAT router to the Internet there remains one other problem - the public IP address may be dynamically allocated, i.e. it may change. There are three options here: tell your users about each change; request a fixed IP address from your ISP (this usually costs extra); or use a dynamic domain name service.

With a dynamic domain name service, a small client program detects each IP address change and informs the service of the new address which updates it's domain name tables. Thus a user can access your server by specifying the domain name which will be translated to an IP address by the dynamic DNS service. Many routers contain a client for several services - check which ones your router supports.