More and more iOS developers who are required to rely upon a device specific identifier for their applications switch from [UIDevice uniqueIdentifier] towards the usage of the device's network card's MAC addresses.
This seems to be the commonly accepted solution if you don't want to or cannot use a GUID.
I can also see, that everybody is checking for the network device with the ID "en0".
Can anybody answer:
I found this question UIDevice uniqueIdentifier Deprecated - What To Do Now? but it does not really deal with the details as I'm asking about.
What is device en0?
Personally I always assumed it means ethernet network, e.g. Linux uses eth0 and BSD-derivates, like OSX, seems to prefer en0, but I could not really confirm it. That's something you can change in most operating systems (but not on iOS, unless jailbroken).
FWIW other people seems to assume the same but I don't consider this a definitive answer. OTOH it should not really matter much ;-)
Is it available on all iPads/iPhones?
AFAIK. Reporting this should be an operating system (not a device) feature and there are no network-less iOS devices (at the moment). I don't have old iOS versions to confirm if it has always been available or not.
Is it available if airplane mode is on or the device is not connected to a network?
Yes, it's available in airplane mode using the NetworkInterface.GetAllNetworkInterfaces () API. Tested with my first gen iPad.