Questions[google-public-dns](server)

Recently we've been having sporadic trouble resolving our subdomain towards 8.8.8.8, so we created a second subdomain for testing, with which we are unable to replicate the issue.

Original subdomain - 42894078.sip.teltel.io - fails occasionally through 8.8.8.8 with the error: server can't find 42894078.sip.teltel.io: NXDOMAIN

Testing subdomain - 42894078.xip.teltel.io - resolves fine through 8.8.8.8

xip.teltel.io is configured exactly as sip.teltel.io.

The only difference is that xip.teltel.io is hosted by DigitalOcean, but sip.teltel.io by AWS.

Do you know why one works but the other doesn't?

During the recent DDoS attack on Dyn servers, many websites couldn't be reached for quite a while. However, these websites were resolvable via Google's public DNS servers. I assume IP addresses were cached for a TTL amount of time since last check that was configured by domain owner via Dyn before it went down, is it correct? If so, does it mean that if someone would use Google's public DNS flush cache tool to flush, say, twitter.com, it would become unavailable for everyone who used Google public DNS as a backup to resolve that domain during the Dyn's downtime?

Back when google first released their 8.8.8.8 and 8.8.4.4 dns servers I did some profiling, and they are way faster for our location. A more recent test confirms this is still the case. However, after careful consideration I declined to make the switch away from our ISP DNS, because looking at a few snapshots of our traffic, so many of our requests were for cdn addresses. Using a central DNS for lookups to CDN sites can produce results that work (and produce the results quickly), but make things slower because they might return less-optimal nodes.

My question, then, was if it was possible to use somehow distinguish CDN network and point those look-ups to my ISP DNS, but point normal look-ups Google's 8.8.8.8 DNS.

Is there any downside to using a public DNS service like Google's 8.8.8.8/8.8.4.4 for corporate network DNS service, as in making it the network connection's DNS server for an AD DC? It seems like if there was not a downside everyone would prefer an easy-to-remember and Googlific service instead of the hodgepodge of ISP specific ones.

Last night we were having some serious server events. At first it appeared that our issue was with google (8.8.8.8). We would run ping and at some point we would have some packet loss. At about the same time our systems would pop a DNS getaddr() exception.

Separately; this is strange to me because I have had to flush my local DNS cache from time to time when my DNS records change at my provider...

Shouldn't my applications and servers, which hit the same 5 remote service providers, have cached the DNS? Why would I get DNS errors instead of network errors?