Let's say I have a domain called example.com. In that domain I have two NS records: internaldns.example.com and externaldns.example.com. I also have A-records that specify the IP addresses for these servers.
But let's say my Name Server internaldns (which is the 1st NS record) contains the following A records:
Now my other Name Server (externaldns, the 2nd NS record) only contains the following A records:
ftp . example.com
Now when someone would enter the URL 'website.example.com', does it first query my first Name Server (internaldns) and then the other Name Server (externaldns), or does it immediately fail if it can't find the requested name on the first server?