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

[Baptiste Jonglez <baptiste () bitsofnetworks org>]

Hi,

While doing statistics on the participants of a public DHT, I was
surprised to see some IP addresses that are not present in the DFZ:

2607:7700:0:25::4e00:605b
2607:7700:0:25::4e25:8ce8
2607:7700:0:25::c808:db2c
2607:7700:0:4::3294:6683
2607:7700:0:4::4c09:4d39
2607:7700:0:4::5985:87d1
2607:7700:0:4::5d7d:3df8

All those IP are in 2607:7700::/32, allocated to T-Mobile USA but never
announced:

  https://stat.ripe.net/2607%3A7700%3A%3A%2F32#tabId=at-a-glance

What could explain their usage in an application?  Some form of address
translation?  Maybe these addresses have been used as source address in
outgoing packets, which would indicate IPv6 tests in T-Mobile? (but
obviously, nobody is able to answer such packets).

Baptiste

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