Dynamic DNS and NAT
There has been tremendous growth in the use of Network Address Translation (NAT) functionality. These devices include Windows machines running Internet Connection Sharing, included in Windows 98SE/Me/2000/XP, or other similar software such as Sygate Home Network. NAT software is also included in most open-source operating systems such as Linux (IP masquerading) or FreeBSD (natd), and is available for other platforms, such as Vicomsoft's Internet Gateway for Macs. More recently, we have seen hardware devices, often referred to as "routers", implementing NAT functionality, such as the Linksys routers, the Netgear Internet Gateway Routers, or the Nexland ISB line.
Many users of various NAT implementations then wonder if it is still possible to use dynamic DNS technology, as implemented in our Dynamic DNS and Custom DNS services, when using NAT. By itself, NAT does not affect dynamic DNS that much, but it does have significant impact on the operation of servers, which is the primary motive for the use of dynamic DNS technology. This white paper will discuss these issues and, whenever possible, make recommendations as to how they can be dealt with. Please note that we do not endorse or provide support for any third-party products that may be mentioned in this article. Also, please note that our discussion of NAT will be limited to the type of NAT where one or more private IPs are converted to one public IP: there are other types of NAT out there, but they are not commonly used in the residential, home office, or small business market.
There are two main challenges involved with using NAT and operating servers with the help of dynamic DNS: ensuring that traffic actually makes it through the NAT and then ensuring that the dynamic DNS hostname/domain is properly updated.
Getting Incoming Traffic Through NAT
Port forwarding is a common method of allowing traffic through specific ports, to a predefined destination within your local network. PortFoward.com offers an expansive collection of tutorials and FAQs related to these NAT issues.
Once you have your port forwarding configured correctly, test it by having someone outside your private network access your servers using your current public IP. Note that many NAT implementations will not let you access things via the public IP from within the private network: that does not mean that they're not accessible from the outside. When setting up port forwarding, what matters is making things reachable from the outside (you can always use the private IPs to refer to things inside the private network). Now, you may finish setting up your hostname/domain.