I dug a bit deeper on the funky connection issue from a DTAG line to my monitoring server.

@domi had already confirmed to me that the EPIX exchange regularly has some funkies with IPv6, so now I wanted to figure out whether this was a regional thing, or the entirety of the DTAG network just doesn't know how to reach the target.

And after I got a generous donation of RIPE Atlas credits to use, I was able to determine just that! (thanks @arch :3)

I ran a probe with a mix of 25 AS3320 (DTAG) nodes and some random worldwide ones.
None of the AS3320 were able to reach my target.

I ran another test with 50 random nodes from Germany and another 50 worldwide.
Some tests from around the world failed, which all don't seem particularly relevant to me.
In Germany? Successful connections from Telefonica, Vodafone, 1&1, Oracle, Netcup, Hetzner, Deutsche Glasfaser, multiple regional providers and even randomly an OpenFactory node.
Who once again didn't manage a single successful connection? DTAG!

IPv4 on the other hand works fine. Even shows a lot less failures around the world.

So yeah, don't know who to blame here, but I was able to confirm that the entirety of the DTAG network has no idea how to reach my monitoring server via IPv6. Fun