Hall I have reset my Fritz box and re-integrated my XBox one, but it doesn't work properly, the wrong IP address is always set. (Usually 192.168.178.18) What should I do now?
This is normal, if it works, isn't it all good? My buddy has a different ip area in his network than me or my parents. This can happen before.
If it works and you don't want to remember the new ip address (for some reason), I'd rather leave it if it works.
Never change a running system!