IOS – How to flush the DNS cache on iOS

dnsios

Similar question to How do I flush the DNS cache on a OS X 10.6 machine?, but for iOS in general.

Specifically, my use case is to flush the DNS cache for applications I downloaded from App Store. Likely apps with native networking implemented (example: apps that use Foundation's NSURLSession).

Running an iPhone 7 on iOS 10.2.1 in China with frequent DNS hijacking happening before you even have time to connect to VPN, so rebooting the device would not be a sufficient solution.

Best Answer

Turn on/off of the Airplane mode in the Settings.app or Control Center makes it fast to flush the DNS cache.

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How to flush the DNS cache on a OS X 10.6 machine

Use

sudo dscacheutil -flushcache

sudo killall -HUP mDNSResponder

In 10.6 the handling of Unicast DNS is now managed by mDNSResponder - dscacheutil -flushcache now just tells mDNSResponder to restart (the second command above).

DNS resolves servers external IP instead of internal IP

It sounds like what you're trying to do is called Split Horizon DNS, and it can be quite tricky. That said, it sounds like you have quite a bit of it already set up but that the internal DNS is not authoritative for your domain.

If you have not already done so, you need to modify your internal DNS to create a primary zone for example.com. Then, when you query for your domain, the DNS should not look outside for an address.

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Related Solutions

How to flush the DNS cache on a OS X 10.6 machine

DNS resolves servers external IP instead of internal IP

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