DNS name server availability Refers to the ability of a public-‐DNS registered “IP address” of a particular name server listed as authoritative for a domain name, to answer DNS queries from an Internet user. All the public DNS-‐registered “IP address” of all name servers of the domain name being monitored shall be tested individually. If 51% or more of the DNS testing probes get undefined/unanswered results from “DNS tests” to a name server “IP address” during a given time, the name server “IP address” will be considered unavailable.
DNS service availability Refers to the ability of the group of listed-‐as-‐authoritative name servers of a particular domain name (e.g., a TLD), to answer DNS queries from DNS probes. For the service to be considered available at a particular moment, at least, two of the delegated name servers registered in the DNS must have successful results from “DNS tests” to each of their public-‐DNS registered “IP addresses” to which the name server resolves. If 51% or more of the DNS testing probes see the service as unavailable during a given time, the DNS service will be considered unavailable.