At WWDC 2015 Apple announced the transition to IPv6-only network services in iOS 9. Starting June 1, 2016 all apps submitted to the App Store must support IPv6-only networking. Most apps will not require any changes because IPv6 is already supported by NSURLSession and CFNetwork APIs.
If your app uses IPv4-specific APIs or hard-coded IP addresses, you will need to make some changes.
What is IPv6?
IPv6 is short for “Internet Protocol Version 6”. IPv6 is the Internet’s next-generation protocol, designed to replace the current Internet Protocol, IP Version 4.
In order to communicate over the Internet, computers and other devices must have sender and receiver addresses. These numeric addresses are known as Internet Protocol addresses. As the Internet and the number of people using it grows exponentially, so does the need for IP addresses.
IPv6 allows more users and devices to communicate on the Internet by using bigger numbers to create IP addresses. Under IPv4, every IP address is 32 bits long, which allows 4.3 billion unique addresses. An example IPv4 address is:
172.16.254.1
In comparison, IPv6 addresses are 128 bits, which allow for approximately three hundred and forty trillion, trillion unique IP addresses. An example IPv6 address is:
2001:db8:ffff:1:201:02ff:fe03:0405
Enabling IPv6 test network from your Mac
One of the hidden features of OS X El Capitan is the ability to enable Internet Sharing to provide only IPv6 addresses. This feature was added to El Capitan to help developers ensure their apps are ready to work with IPv6. It uses NAT64, which facilitates communication between IPv6 and IPv4 hosts by using a form of NAT.
- Boot OS X 10.11
- Make sure your Mac is connected to the Internet, but not through Wi-Fi.
- Launch System Preferences from your Dock, LaunchPad, or the Apple menu.
- Press the Option key and click Sharing. Don’t release the Option key yet.
- Select Internet Sharing in the list of sharing services.
- Release the Option key.
- Select the Create NAT64 Network checkbox.
- Choose the network interface that provides your Internet connection, such as Thunderbolt Ethernet.
- Select the Wi-Fi checkbox.
- Click Wi-Fi Options, and configure the network name and security options for your network.
- Setting up local Wi-Fi network options
- Select the Internet Sharing checkbox to enable your local network.
- When prompted to confirm you want to begin sharing, click Start.
- Once sharing is active, you should see a green status light and a label that says Internet Sharing: On. In the Wi-Fi menu, you will also see a small, faint arrow pointing up, indicating that Internet Sharing is enabled. You now have an IPv6 NAT64 network and can connect to it from other devices in order to test your app.
Important: To ensure that testing takes place strictly on the local IPv6 network, make sure your test devices don’t have other active network interfaces. For example, if you are testing with an iOS device, make sure cellular service is disabled so you are only testing over Wi-Fi.
To test your IPv6 connectivity, you can visit Test your IPv6.
Testing Your App on the IPv6 Network
By enabling Create IPv6 Only Network, Internet Sharing will set up the following:
DNS64
NAT64
Use the NAT64 Network for app testing.
Make NAT64 testing part of your regular development process.
What breaks?
IPv4-only storage objects
IPv4-only APIs
IPv4-only usage of an API
Pre-Flight checks before connecting
– Checking to see if a device has an IPv4 address
– Checking to see if a device has a 0.0.0.0 address
Address-family agnostic code
Connect without preflight
– If connection succeeds, great
– If connection doesn’t succeed, handle the failure gracefully
Use higher-level networking frameworks
– NSURLSession and CFNetwork-layer APIs
RFC 4038 “Application Aspects of IPv6 Transition”
Connect-by-name APIs – Use DNS hostnames wherever possible instead of IP addresses.
IPv4 literals in NAT64+DNS64 networks
New for 10.11 and iOS 9
Use higher-level networking frameworks
– NSURLSession and CFNetwork-layer APIs
Client supplies IPv4 address Literal
– OS synthesizes IPv6 address
