CoDNS dramatically improves DNS reliability, measured by the local nameserver availability. To quantify this effect, we measured the availability of name lookups for one month across all CoDeeN nodes, with and without CoDNS. We assume that a nameserver is available unless it fails to answer requests. If it fails, we consider the periods of time when no requests were answered as its unavailability. Each period is capped at a maximum of five seconds, and the total unavailability is measured as the sum of the unavailable periods. This data, shown in Figure 18, is presented using the reliability metric of ``9's'' of availability. Regular DNS achieves 99% availability on about 60% of the nodes, which means roughly 14 minutes per day of no service. In contrast, CoDNS is able to achieve over 99.9% availability on over 70% of nodes, reducing downtimes to less than 90 seconds per day. On some nodes, the availability approaches 99.99%, or roughly 9 seconds of unavailability per day. CoDNS provides roughly an additional '9' of availability, without any modifications to the local DNS infrastructure.
