IPv6 prefix from T-Mobile USA used but not announced in BGP (2607:7700::/32)

Aaron Hopkins lists at die.net
Wed Apr 27 23:40:38 UTC 2016

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

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