@HighCommand 

I have yet to see my R605 use the secondary DNS, it always goes to primary every time.  Granted only been using the device 6 months

However from experience with other vendors and such, the secondary DNS is only ever accessed should the primary fail to respond within an accepted heartbeat.   They usually tend to revert back to the primary at reboot or periodically when its available again.

@Philbert It did not worked that way in my case. I have primary DNS setup pointing to my AdGuard DNS, secondary to OpenDNS. Anytime primary fails (like - server is down) secondary is not used and therefore non network traffic is possiblem...

@Norbert_123 

Strange i cant recreate that.   Curiosity got the better of me so I pulled the LAN on my Primary, it took a few mins but did go to the secondary.  DNS just set on the controller, nothing fancy

@Virgo 

You misunderstand the question.  DNS is working ok.  I want to know how the software is designed.

Does the primary get 100% of the traffic when working and the backup only used when primary is down?

Do primary and secondary load share with some form of round robin or other load sharing protocol?

Is the method just random?

I have a server handling DNS and my router is pointed at that.  I want 100% of the traffic going through my server.  If some of the traffic goes through the backup it will not be logged.  If my DNS server fails then I want the backup to work until the failed server is remediated.

The developers who worked on the this segment of the code had to have a specification or use case that they worked to.  I would like to know so that I get the results expected from my configuration.

Basically, if the operation is other than case 1 then I need redundancy with my DNS server.

Thanks