How to Link a Domain Name to a Dynamic IP - The Theory
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We’re going to keep the theory to a minimum; that's a promise! First, domain names are held in a so-called name server. Thanks to domain names we can enter names in our browsers for URLs without being required to memorize those IP digits. In our everyday lives, software such as web browsers and mail clients handle the DNS resolutions. We call “resolution” the necessary process of discovering the IP to which a domain name points.
To simplify this, imagine the following: the DNS server is a huge server with hundreds of entries containing the appropriate IP addresses for each domain name. This is straightforward in the case of static IP addresses. However, this gets trickier when it deals with dynamic IPs because the server must be notified in real-time to update its entries. It must also be told that the maximum caching time should be set to a minimum.
The DNS cache was designed to reduce the load on DNS servers. There is a specific TTL (time to live) time interval during which a DNS is “valid.” The TTL is the maximum amount of transmissions (iterations). Until this limit is reached (TTL expires), a “resolution” can be cached -- meaning that clients won’t request an update.
As mentioned earlier, with dynamic IPs, the main name space server must be notified as soon as possible, whenever the IP address changes, to update its records immediately. DNS services that provide Dynamic DNS services too also usually supply a client-side application that manages these queries (if another IP change occurs then notify the name server). This is the whole system in a nutshell.
Networking components such as routers, for example, that have DDNS as an built-in feature are usually assigned to a predefined name space server. That’s the way their firmware was designed, and dynamic IP assignments are told to the DNS hosting service. This eliminates the need to run the stand-alone “ddclient” application.
The aforementioned DDNS client is often called a ddclient (Linux client). Another network maintenance utility which is widely used is the nsupdate. Using the latter to notify and execute update queries on name space servers requires appropriate security measures (authentication and permissions by DNSSEC), i.e.: HMAC-MD5 hash keys.
In the next section we’ll talk about practical real-world applications. Until then, please glance over to the diagram below. By now you should understand how DDNS works but a diagram like this may help to plant the whole concept in your long-term memory. As you can see, the ddclient notifies the DNS server (name space server); in the diagram, this is show as the new IP variable written right on the arrow.
(Amateur sketch done in less than a minute)
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