Indeed it is DNS rebind protection.
I use wildcard on my Fritzbox. I added *.mydomain.com
and my MyFritz address *.er467.myfritz.net
Important for everyone who makes changes on DNS rebind protection: You will need to completely RESTART your Fritzbox. Even if you add a line, or edit. One domain per line. It will not work without it ☝🏻
Looks interesting ☝🏻😃
Will try it out