On Wed, 27 Apr 2016, Baptiste Jonglez wrote:
So, if this is basically DNS64/NAT64, these IP addresses should not be seen as source or destination address outside of T-Mobile's network, and are not attached to the interface of any device.
Based on http://dan.drown.org/android/clat/, it looks like it may be possible for an IPv4-only application to connect to raw IPv4 addresses through a IPv4-to-IPv6 NAT service on the Android device itself, which then is transported over IPv6 to T-mobile's IPv6-to-IPv4 NAT device. Skimming https://github.com/savoirfairelinux/opendht/blob/master/src/dht.cpp, my guess is that new peers find your IPv4 address:port (on T-mobile's IPv6-to-IPv4 NAT device) in the DHT and contact you, which somehow doesn't get correctly translated back to IPv4 before it makes it to your application, so you are seeing the untranslated IPv6 address. Replying to the new peer on the T-mobile-internal IPv6 address should still work as long as you stay on T-mobile's network but are of limited use otherwise. -- Aaron