DNS zone servicing concepts

Question

Currently I am working out some concepts about how DNS works and am running into a question I can't easily find an answer to on the internet. I am looking for an answer based on a set of questions regarding the following scenario:

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Server01.example.local and server02.example.local are both generic DNS (BIND, Windows, etc.) servers. They both live under the impression that they are authoritative primary for the zone example.local. There is a working network connection between these two servers.

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1. First of all; Is this configuration possible? Is it possible to host two R/W copies of a DNS zone?
2. If it is possible, do problems arise as both servers service the zone as R/W primary? Thus instead of having a secondary server.
3. What would happen if the zonedata on both servers for example.local would be different and clients get serviced over a virtual IP? This would be a loadbalanced configuration I suppose.

As my mobile phone can't virtualize two DNS servers (as of yet), I can't truely test this. Can someone shed some light on this?

Thanks in advance.

Answer 1

1/ Yes that is perfectly possible, and this is one of the reasons that registrars and a recognized authorities (IANA, ...) exist for public DNS zones.

2/ There is no real issue with that if you have not done any further configuration. Problems arise when a parent server has to communicate to clients the IP of the server that really "owns" the domain. Technically speaking it is possible to register the domain on both servers AND advertise them both, but you could encounter what is called a split-brain configuration: depending on which you are requesting, you might have wrong answers; if server A was updated but not B, a client requesting something from server B would get an inaccurate answer.

3/ See my previous answer. And add several things like: incorrect cache, non DNS-queries (ie. webservers, mail, SIP, ...) failing from time to time with no apparent reason, and many more.

Final point: This configuration should not be done , at least manually. Some tools / professional application allow you to do this but they ensure that everything is correctly replicated to avoid unsolvable issues. If you wanted something resilient, you'd rather go with a Master/Slave configuration and if your master were to die a simple change in the slave's configuration would make it the authority server.