I am developing web apps, and using different IP addresses to download new software as well as test against our hosted servers. What I have found is that I can resolve addresses in some cases against Google's PD DNS (18.104.22.168) but not others, specifically I had problems acquiring patches from Microsoft, who advised on their technical support to use 22.214.171.124 which worked (for me).
But then after using the recommended DNS from Microsoft, my hosted servers could not be resolved. I addressed this by using both DNS IP Addresses in primary and secondary settings. But shouldn't all PD DNS' be able to resolve all addresses ? If not why ? This could be a very broad question, so if you have references to explain this, please link them in your answer.)