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1 have 3 dns servers with names:

ns1.example1.com ns2.example1.com ns3.example1.com

ns1.example1.com is cPanel based server, while ns2 and ns3 are cPanel DNSOnly machines.

I also have a domain, example2.com . That domain name servers are:

ns1.example1.com ns2.example1.com ns3.example1.com

All subdomains of example2.com (*.example2.com) are also on these name servers.

Some time ago ns1 server went down, and after few minutes customers started complaining, that example2.com domain is unreachable. After some time ns1 server was back online, and complains stopped.

Now I'm trying to test how could that happen, so I stop "named" service on ns1. On my local machine, and on some of my servers, domain example2.com and all of subdomains still resolves correctly (maybe because of caching?). But when I use some dns checker like dnschecker.org , or any other, it says that some dns servers are not able to get example2.com domain IP (or any other subdomain).

The question is why turning off one of name servers is causing domain example2.com to be unreachable? Isn't it why I have 3 name servers to provide IP address when ns1 (or any other) is down?

When I'm using dig example2.com it still gets back with correct IP result. So is my domain reachable for everyone? Or not?

  • If you gave the real names one could have explained to you better what the problem is, with specific information on glue records, if needed. – Patrick Mevzek Dec 12 '19 at 18:39
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All 3 ns servers really have different 2nd level domain?

Maybe it should be ns1.example1.com, ns2.example1.com, ns3.example1.com?

If it's ok, then check every ns response from internet / external network:

nslookup example2.com ns1.example1.com nslookup example2.com ns2.example2.com nslookup example2.com ns3.example3.com

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  • You're right, my mistake, I corrected my question. – m_per Dec 12 '19 at 9:45
  • All the commands above return (when ns1 is down) with nslookup: couldn't get address for 'ns1.example.com': failure, nslookup: couldn't get address for 'ns2.example.com': failure nslookup: couldn't get address for 'ns3.example.com': failure. So it seems it can't resolve any name server IP address when ns1 is down. – m_per Dec 12 '19 at 10:54
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It seems that tld nameservers didn't have something that is called GLUE records. After setting it up in domain provider panel (and having to contact them to make it work) it seems it's working fine. Big thanks to Vadim as my answer was found when I noticed that nslookup can not resolve any ns*.example.com , that lead me straight to the point, and I got that idea from you!

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