What is SmartCache?
SmartCache - Here's how it works: When an authoritative DNS provider suffers an outage, all of the Websites it provides service for are taken offline. They are inaccessible for everyone on the Internet. But no longer for OpenDNS users. Our servers will now immediately look for the last known good address for the site in our caches, and use that to load the site. So effectively OpenDNS users will be able to access Websites that appear down for everyone else. For our millions of users saving them Internet access interruptions and the time they waste is invaluable.
The OpenDNS network receives billons DNS queries daily our users and their devices (referred to as a stub client in our world). When each subsequent DNS query is received, OpenDNS name servers already know the answer (much more often than your regional ISP name servers). Hence, users do not wait on the authoritative name servers to return this same answer. OpenDNS knows nearly every publicly addressable host’s IP address Internet-wide at any given time.
However, this is not what makes the caching technology unique. Many authoritative DNS outages, attacks or failures have impacted business-critical content servers such as salesforce.com, amazon.com and petco.com. Or even millions of domains, for example, when the entire top-level domain used by Germany (.de) became unreachable. When such incidents occur – which is not uncommon – the OpenDNS network still returns the last-known correct address using exclusive caching logic.
SmartCache is turned on by default for all users and only applies to queries where the authoritative server hands back a SERVFAIL response code or the query simply goes unanswered.