If you need to iPhone DNS cache clear to change its settings or set custom DNS lookup here are two fastest methods to do it with ease.
Remember that these two methods work the same for all iOS devices. The Airplane Mode approach works particularly good with iPhone and with cellular equipped iPad devices. Before we start you can read how to get access to iCloud locked device using DNS server.
This first method is preferential as it has the least amount of impact overall to other activity on the iOS device because it doesn't require a reboot.
Step 1. To reveal Control Center swipe up from the bottom of the iPhone screen.
Step 2. To enable Airplane Mode click on the Airplane Icon. Now please wait till the devices radio signals will be off as indicated by the airplane logo in the status bar and next please click again on the Airplane Icon to disable Airplane Mode.
Step 3. Swipe down to leave Control Center, the DNS cache has been flushed successfully
Now you have clean iPhone DNS cache, whatever adjustments were made in the devices Network
Settings will take effect immediately without any further action.
Very rare the Airplane Mode toggle does not work successfully to clear out some persistent DNS caches. It can be a bug that's why it does not work sufficiently. In this case, you have another method to clear iPhone DNS cache.
This method includes resetting the iOS devices network settings to flush all old DNS settings. The only minus is that you’ll lose connections to Wi-Fi routers and other specific network settings. It also reboots the device, which is actually other way to clear DNS cache anyway.
Step 1. Launch the “Settings” app in iOS and navigate to “General” followed by “Reset”
Step 2. Pick “Reset Network Settings” option and confirm that you want to clear out all network settings.
Step 3. After your iPhone will be rebooted, you will get clean iPhone DNS cache together with all other customizations. It mean that you’d need to set a manual change made to DNS servers again
The work is done.
This approach is very rarely necessary, and though it’s more complicated than the AirPlane switch or the Mac command line approach offered to flush DNS details in new versions of OS X, it does work if all else fails.