Why pay for a distributed DNS service when ISPs cache lookups?

Question

Suppose I've purchased example.com from my neighbor's startup domain name company, superlowcostdomainnames.com (aka SlowDNS).

At first DNS is a bit of a performance drag, because SlowDNSs servers are all hosted in my neighbor's basement. My site only got ~100 visits per day, so ISPs often didn't have the domain name record cached. The requests would travel all the way to my neighbor's basement.

But now example.com has taken off and is receiving hundreds of thousands of visits every day. I suppose it must be the attractive combination of rounded corners and a beige background.

So now, most DNS requests are fast, since they're cached at the ISP.

But a representative for SkyFlashCDN is trying to sell me their distributed DNS service. Instead of requests traveling to my neighbor's basement, they'll be serviced by "one of 1138 data centers around the world."

My site is popular, and ISPs are basically functioning as a distributed DNS service. Why would I pay for the service when I'm (apparently) getting the equivalent for free? Is there some performance benefit I'm missing?

Answer 1

You shouldn't host DNS in your basement. At a minimum you should have 3 DNS servers located in different geographic locations. Otherwise DNS is a single point of failure. Your website could easily be knocked offline by:

• A power outage in a single location
• A network outage in a single location
• A single computer crash
• A denial of service attack against DNS
• A single hacker

Basic but robust DNS services are super cheap. You can get get DNS hosting for $10 or $20 per year. Such services are often bundled with domain registration or web hosting. There is really no reason to host DNS yourself in your basement.

I don't see a lot of benefit from moving from 3 nameservers to thousands though. As you point out, DNS requests are often cached, and DNS performance is rarely bad enough to cause perceivable performance problems for the site as a whole.