Question Weird IPv6 in Error Log

[cyxxnet]

I checked the error logs for a few domains today. I noticed something that I don't understand how something like this is even possible.
In my opinion, this is not a valid IPv6 address.
But how do you manage to connect to a server with such addresses so that it shows up in the logs?

[authz_core:error] [pid 298052:tid 140669777508032] [client 2a06:e80:3000:1:bad:babe:ca11:911:0]

 

[Peter Debik]

It's valid basically. The first four groups are often the unique subnet for a user. The following groups can be assigned by the user himself. It's not completely out of the world, but a really strange idea.