If you want to give yourself a migraine, Microsoft has a comprehensive document[0]. DNS/AD has been the focus of my job for the last 5 years and I'm still not a

If you want to give yourself a migraine, Microsoft has a comprehensive document[0]. DNS/AD has been the focus of my job for the last 5 years and I'm still not absolutely certain the circumstances that a given Windows client will return to the 1st candidate DNS server when there are > 2. On Unix-y things, resolv.conf is specified to be used in the listed order[1]. Local caching resolvers will default to remembering the last successful server and treating the list as circular, so after the first DNS server has a failure it won't be tried again until each subsequent server has failed. Every time a distro has switched to having a local caching resolver by default you'll find big threads of people confused over the altered behavior[2]. And default behaviors are meant to be over-ridden, so in places where I have dnsmasq providing DNS for a network (PiHole, EdgeRouters) I set all-servers[3] so that every upstream is queried simultaneously and the fastest response wins -- an exceptionally bad configuration option when having upstreams with differing views of DNS, but for the general use case it makes the Which public DNS is fastest debate moot. [0] https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2008-R2-and-2008/dd197552(v=ws.10) https://docs.microsoft.com/en-us/previous-versions/windows/i... [1] http://man7.org/linux/man-pages/man5/resolv.conf.5.html http://man7.org/linux/man-pages/man5/resolv.conf.5.html [2] https://github.com/systemd/systemd/issues/5755 https://github.com/systemd/systemd/issues/5755 [3] http://www.thekelleys.org.uk/dnsmasq/docs/dnsmasq-man.html http://www.thekelleys.org.uk/dnsmasq/docs/dnsmasq-man.html