DNS

What is a dns server?
It is used to resolve name in your network and resolve internet adresses

Many poeple make the bad configuration that follow:
In their local network card, in IPV4 config, in DNS configuration.
They put in the dns server 8.8.8.8 and 8.8.4.4 (google's dns servers)
If you do that, your own computer will not be able to communicate with your domain server fully.

Now something even worst.
In the IPV4 network card configuration, some poeple put in their DNS servers some external dns servers adresses. You cannot do that. That is not how a dns server work. The dns server will have forwarders to go outside your network, but it need to go inside first in the IPV4 config of it's own network card. In IPV4 dns list, it must point to itself.

Your DNS server, will allow all the computers on your local network to communicate only if you resolve himself before going outside. Your DNS server have the list of all the names on your network and their ip adresses. But if you ask him to search on an external dns server first, no computer will be found. Only web pages. Oh great, your internet will work... but your local network will not perform very good...

If you have two dns servers, In IPV4 config, They should point to each others first.

After that, your internet provider should be the one giving you the DNS path to follow. Geographically. Why not jump directly to the united states? Because if a road get broken, you must find another road to go to your destination. Now if you are in Canada and go directly to the us, and one road break. You will not be able to resolve names to your destination.

If you follow a geographical path (nearest DNS server first, aka, your internet's provider DNS) then you will see the signs "road broken, please take this alternate road".

STOP putting external DNS everywhere in a local network! Please! :)