DNS stuck? (iOS 8.1 and OS X 10.6.8)

DNS routing tables, cache, and Apple iOS/OS X anomalies? Obsolete DNS records? Spurious, temporary DNS errors?

This was a temporary (48-hour) problem, but it is recurrent, and I am trying to understand what causes this, and a good workaround for next time. Long story, sorry, but if you are a DNS expert, this may be interesting... It's a mystery to me.

The Situation:

While transitioning a domain name from one DNS name server to another, there was a DNS anomaly both on OS X (MacBook Pro) and iOS (iPad) devices which had accessed the old websites just before the switching of DNS name servers to a different host. Both OS X and iOS were behaving as if these devices were holding DNS records in a cache and would not update them, in spite of multiple reboots. Seems strange.

Recently, this happened more than once, with four different domain names, over a period of several weeks, while switching registrars. The old registrar (Godaddy) deleted the DNS records just before the DNS was set up with the new registrar. (Yes, this issue could have been avoided if the DNS host were different from the domain registrar, but these sites were not mission-critical and were setup for highest simplicity.)

The expected result was that each website would “disappear” for a short time — hours not days — and then reappear. The TTL value for the old DNS records was one hour. It took me about 15 or 20 minutes to make the DNS record changes as soon as the new registrar picked up each domain name. Nothing too unusual here. The websites should've been down for no more than a few hours.

However, these websites went down for 48 hours, in each instance, but only for those Apple devices which had recently accessed the websites. (So, it's not the router, gateway, or the ISP cache, it's the OS/device itself, it seems.)

For a period of about 48 hours, none of these iOS/OS X devices (which had recently accessed the old website) could find the new DNS records. Both Chrome and Safari reported errors, the site could not be found. This happened in every instance, for each of these four websites. Rebooting the devices did not help. Resetting the Wi-Fi modem/router did not help. Other devices which had NOT accessed the old website had no problems opening the website normally, via the new name servers. Any iOS device which had accessed the old website had problems — for two days — before it could access the website.

Other devices (which had not recently accessed these sites) had no problems accessing these websites very shortly after the DNS was set up with the new name server. These were all using the SAME Wi-Fi router, so it must be an OS problem, not an ISP cache problem.

Switching from Wi-Fi to cellular (on any affected iOS device) instantly corrected the problem. Presto, the websites were found. But, the DNS problems immediately returned when switching back to Wi-Fi —— Cellular okay — Wi-Fi not okay —— Repeat.

After 48 hours, DNS propagation was fine again, for each of these strange cases. The DNS caching problems had eventually gone away.

What's going on here? It seems that the old DNS routing tables may persist for 48 hours —— even when the DNS changes have been effective on all other devices —— AND ALL DEVICES AND ROUTERS WERE REBOOTED. Yes, I also switched to Airplane mode to try to flush the DNS cache on iOS. No joy.

Questions:

Is this a known DNS cache problem? How can the DNS cache survive a reboot? Is there an easy way to flush the DNS cache on any iOS device?

Next time, try changing the iOS device DHCP DNS server to 8.8.8.8 or 8.8.4.4 (Google DNS) and see what happens?

Would using a VPN or an HTTP Proxy resolve these temporary DNS problems? I wanted to test the websites on iOS, but had to wait 48 hours.

I am hoping that a DNS expert with iOS/OS X expertise will help explain this situation, and offer some proper workarounds.

{{ iOS 8.1 on 128GB iPad Air; OS X 10.6.8 Snow Leopard on MacBook Pro, 8GB RAM; ISP = Sonic.net }}