At the registration stage, by transport ipv6, sipgate.de makes two endpoints with addresses
Contact:
<sip:4655310@[2a03:f540:1:1100::181d]:5060>;expires=597;received="sip:[2A03:F540:1:1100:0:0:0:181D]:5060",
<sip:4655310@[2A03:F540:1:1100:0:0:0:181D]:5060>;expires=600
How is that?
Moreover, the registration expire time soon decreases to 149 seconds, which I don't really like.