If you monitor your external Internet connectivity, you may wonder which machine is the best to ping. Hesitate no more - you can use RIPE Atlas anchors as landmarks.
I work at AFNIC (the registry of .fr domain names), in the R&D department, on, among other things, DNS, security, statistics.
Pages created by Stéphane Bortzmeyer
The techniques used by the L-root DNS server are documented in RFC 7108 "A Summary of Various Mechanisms Deployed at L-Root for the Identification of Anycast Nodes". These techniques can be used by the RIPE Atlas probes to find the instance of L-root they are talking to.
Each RIPE Atlas probe has at least one DNS resolver, indicated by a DHCP reply on the local network of the probe. Irrespective of the IP address of the resolver, this server may have IPv4 and IPv6 connectivity or only IPv4 connectivity. What is the percentage among RIPE Atlas probes?
In theory, all IP addresses are the same, and you can allocate them at random without a problem. 192.168.1.2 is certainly not better or worse than 192.168.1.15, right? But, in practice, certain IP addresses are regarded as "special" by some implementations and do not yield the same user experience. This is the case for the "dot-zero", IPv4 addresses in which the last byte is zero.
To check the connectivity of an IPv6 device with RIPE Atlas, one typically asks N probes to ping the target and deduces the reachability of the target from the percentage of failures. But RIPE Atlas probes, like many IPv6 devices, often believe they are IPv6-connected while they are not.
A DNS anycast name server has several physical instances, all behind the same IP address. Which one is used by a RIPE Atlas probe depends on the location of the probe in the BGP space. RIPE Atlas can query the physical identity of the probe and therefore help to determine which instances have the largest user base.