Supporting IPv6-only Networks
Supporting IPv6-only Networks - Support - Apple Developer https://developer.apple.com/support/ipv6/
Starting June 1, 2016, all apps submitted to the App Store must support IPv6-only networking. A majority of apps will not require any changes as IPv6 is already supported by NSURLSession and CFNetwork APIs. However, if your app utilizes IPv4-specific APIs or hard-coded IP addresses, you will need to make changes. Be sure to test for IPv6 compatibility before submitting your app to the App Store for review.
For more information on supporting IPv6 networks, review Supporting IPv6 DNS64/NAT64 Networks.