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Connecting sites with dynamic IP addresses across the Internet

How can I connect sites across the Internet when their public IP addresses change fairly often?

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You need Dynamic DNS. DNS (Domain Name System) stores mappings between domain names, such as, and its corresponding IP address, in this case. The idea is that names such as are easier for humans to remember and work with than the associated IP address. In the normal case of a site with a static (fixed) IP address, the domain-to-IP address mapping is entered into DNS and rarely requires any further attention from the site operator. Sites with dynamic IP addresses, such as those provided by Cable/DSL ISPs to home users, have to deal with the fact that their IP address (and thus the domain-to-IP address mapping) can change frequently.

The problem of frequently changing IP addresses is handled nicely with Dynamic DNS, a service available for free or at nominal cost by several providers. With Dynamic DNS, the site with the dynamic IP address runs a small script or program that monitors the site's IP address and notifies the Dynamic DNS provider when it changes. The provider updates its DNS mappings on the fly, so that users can still find the site after an IP address change. Note that the Dynamic DNS providers are usually distinct from the ISP and can therefore work well with your customer's current network environment.

This was first published in October 2006

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