DDNS – Dynamic DNS Service – Hype?

It seems there is a lot of demand for DDNS – Dynamic DNS Service. If you pop “DDNS” into Google, you’ll be surprised with the listing of articles you’ll find (including a Wikipedia one) describing what dynamic DNS is and how it can be beneficial to you when hosting servers behind IP addresses that frequently and randomly change. We even found an entire list of DDNS providers, many of which offer the service for free. So that begs the question…

Why such a demand for Dynamic DNS?

We at Total Uptime really can’t understand why there is such a demand for this type of service. Perhaps that curiosity is a result of the fact that it grates against our corporate goal of helping our clients achieve 100% uptime, where anything dynamic in nature – especially related to DNS – seems radically counterintuitive. After all, we’ve talked about the dreaded TTL issue in prior articles that can affect web applications, so why would you want to expose yourself to short, yet frequent outages?

The other question worth asking is “What type of provider delivers dynamic IP addresses?” The only ones we can think of are Dial-up, DSL, cable and Satellite Internet providers. So for fun, we asked around to see what someone might actually do with a DNS hostname associated with ‘no IP address in particular’. Much to our surprise, there were quite a number of interesting responses:

• To host a mail server
• To host a web server
• To use a cloud server on DHCP
• To access a remote desktop
• To access remote cameras for viewing

… and the list went on…

Of course, our natural assumption was that these sorts of items were being hosted or accessed at home, but sadly that was not the case. More often than not, businesses were actually using dynamic IP addresses for their office applications. But why? Are providers no longer offering static IP addresses? Is the shortage of IPv4 space making providers stingy?

For the most part, the answer was simple. It was all about ‘cost’. Organizations said they were simply avoiding the fees associated with obtaining a static IP address from their provider. So when we spoke to a couple of them to find out why the cost of static IP addresses was so high, we were a little perplexed to learn that it was in the neighborhood of an extra $20 to $30 per month on average.

One customer we spoke to said that the cloud computing provider they used did not provide static IP addresses and that every time the machine restarted, it was given a new IP. Wow!

Considering the fact that a static IP address with most providers is pretty cheap, we thought we should revisit the cost of downtime, because obviously that is not a significant concern to the organizations choosing to host what we consider to be critical applications behind constantly changing IP addresses. Let’s assume the IP address changes once per week. Some providers state that they give them out for 24 hours, and some state they give them out for weeks at a time, so we’ll use a week as a reasonable average for some fun calculations.

Assuming a TTL value of 60 seconds for the associated ‘A’ record pointing to the dynamic IP, one could expect anywhere from a few minutes to as much as 30 minutes of downtime every week. This is due to the fact that time is required for the dynamic IP agent to detect the change and update the DNS server, and then the dreaded TTL issue drags the outage out for a little longer until the cache has cleared all over the Internet.

If we assume the above process can take 15 minutes and that the IP changes once per week, that adds up to a total of 780 minutes of downtime per year, or 13 hours which is 98.19% uptime. Ouch! That doesn’t even come close to 100%. I guess 99.99% isn’t even a dream at that point. If we take a more conservative approach and assume only 5 minutes of downtime per week, which is the absolute minimum we can imagine, that is 260 minutes of downtime or 4.33 hours per year, which doesn’t even bring it up to 99.5% uptime.

I suppose if you’re using the hostname to access your remote desktop or just to view some cameras at home or the office, it probably impacts only yourself and isn’t a big deal. We can understand that and I suppose that the dynamic DNS entry is almost a necessity and quite handy to make accessing things easier. But so many businesses stated they were also hosting web and email servers behind these constantly changing IPs. That is something we simply do not understand. Perhaps the associated downtime is something that simply doesn’t matter.

People have asked why we do not offer a dynamic DNS service, and we hope that this article addresses that question a little bit. If we were a provider of DNS services for anything other than organizations wishing to achieve 100% uptime, we might offer DDNS. But we’re not and as a result, demand for it is low here at Total Uptime.

We hope our candid review of DDNS has been somewhat helpful for those considering its use.