My ISP only provides me with an IP4 adress, but Deluge (Torrent-Client) lists IP6 adresses in the peers tab. How does this work? I thought to not be able to communicate with IP6 devices.
Usually this is because of the automatic IPv6-in-IPv4 Teredo tunneling in Windows. It not reliable for normal use but as BitTorrent distributes the load across many connection anyway some of those Teredo connections might actually work :-)
Windows systems only try to use Teredo when connecting explicitly to an IPv6 address when no other IPv6 access is available. Teredo won't be used when connecting to a hostname instead of an explicit address.