Exactly, that was my point: the 6to4 address 2002:ac8:5ac5:0:b0:46d:fd08:7c9f actually means that the originator is 10.200.90.197 (ac8:5ac5). Being a private address I don’t think it is valid as a 6to4 address source, because they are meant for public IPv4 addresses: The document defines a method for assigning an interim unique IPv6 address prefix to any site that currently has at least one globally unique IPv4 address, and specifies an encapsulation mechanism for transmitting IPv6 packets using such a prefix over the global IPv4 network. It seems to me is generated by IONOS/Kundenserver. It looks to me like they are using internal email servers for customers and instead of properly configuring IPv6, they allow 6to4 addresses to be generated or may be they do it on purpose. The interesting thing is that afterwards they send the email via IPv4 only! So either you configure IPv6 properly all the way thru, or not at all, but this way using an invalid 6to4 address is very weird and definitively not a good practice. May be someone has contact with them so they realize this is broken. Regards, Jordi @jordipalet
El 21 ene 2025, a las 19:19, Gert Doering <gert@space.net> escribió:
Hi,
On Tue, Jan 21, 2025 at 04:03:53PM +0100, Marco Moock wrote:
6to4 with private IPv4 address in the inside.
I don't see any problem here.
Why would anyone do this?
If you only have v4, use v4, not pretend to have v6. If you have real v6, do not use 2002:
Gert Doering -- NetMaster -- have you enabled IPv6 on something today...?
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