The DNS study of the top 1,000 sites ranked by Web information company Alexa showed that internally managed and ISP-managed global domains were available an average 99.7% of the time, or more than 4 minutes of downtime per day. Externally managed domains were available an average 99.85% of the time, just over 2 minutes of downtime daily.
The Verisign report notes that even a few minutes downtime can cost thousands, or even tens of thousands, of dollars per day on high-volume websites. The availability for U.S. domains was higher than the global average for both internally/ISP-managed and externally managed domains.
The report speculates that DNS service providers have higher availability because of their use of Anycast DNS resolution, which assures there is always a server available to respond to DNS queries. Verisign combined the data for both locally managed domains and those managed by ISPs under internal because most ISPs don't invest heavily in assuring maximum availability, says Sean Leach, Verisign VP of technology with the network intelligence and availability group.
"For ISPs, DNS is really a cost center," he said. "It's something they have to provide; it doesn't make them any money. Some ISPs do a very good job, but for the vast majority, it's an afterthought." Verisign manages top-level domains including .com, .net, .gov and .edu through its services.