A DNS sinkhole, also known as a sinkhole server, Internet sinkhole, or Blackhole DNS[1] is a Domain Name System (DNS) server that has been configured to hand out non-routable addresses for a certain set of domain names. Computers that use the sinkhole fail to access the real site.[2] The higher up the DNS resolution chain the sinkhole is, the more requests will fail, because of the greater number of lower nameservers that in turn serve a greater number of clients. Some of the larger botnets have been made unusable by top-level domain sinkholes that span the entire Internet.[3] DNS Sinkholes are effective at detecting and blocking bots and other malicious traffic.
By default, the local hosts file on a computer is checked before DNS servers, and can be used to block sites in the same way.
Applications
Sinkholes can be used both constructively, to contain threats such as WannaCry[4] and Avalanche,[5][6] and destructively, for example disrupting DNS services in a DoS attack.[clarification needed]
DNS sinkholing can be used to protect users by intercepting DNS request attempting to connect to known malicious domains and instead returning an IP address of a sinkhole server defined by the DNS sinkhole administrator.[7] One example of blocking malicious domains is to stop botnets, by interrupting the DNS names the botnet is programmed to use for coordination.[8] Another use is to block ad serving sites, either using a hosts file-based sinkhole[9] or by locally running a DNS server (e.g., using a Pi-hole). Local DNS servers effectively block ads for all devices on the network.[10]
