In my set up I have 3 sets of mikrotiks, each set contains 2 routers for HA.. Not relevant.
First set is the office network, second set the DC and third one is within testlab.
Office and DC setup is with OS version of 4.11, testlab 4.16.
Office has configured DNS with multiple dns servers. Those servers are the DC, testlab and some external DNS server.. DC and Teslab has some custom domains configured - static addresses. When i set up resolv.conf to be the office dns, everything get resolve ok except the testlab. When i set up dns to be the DC, everything get resolved ok except the testlab.
Testlab static entries are sometimes resolved, sometimes not, when they are resolved, they stay in the cache for TTL period of the time. When they are cleared, they dont have to be cached again, but might.
When i moved the static entries from testlab to DC (this is not a solution i am looking for), everything works perfect. Even if my resolv.conf is set up for office mikrotik.
Maybe it is a problem of 4.16 OS , i dont know. When i run dig command @testlab dns, it works. but when i am access dns through office mikrotik, which looks for this entry in testlab mikrotik, it randomly get the IP resulved.
If it wouldnt get ever resolved, i would say it is a firewall issue, but based on this, i think it is a glitch somewhere between mikrotiks. I would say it might be a problem with 4.16 OS, but never tested testlab running with 4.11 OS before with this kind of DNS configuration.