Don't stress yourself, you'll end up getting headache.
Instead of using letter IP address, simply use numbers (e.g. 216.58.210.142).
login01.tibia.com = 17 letters
216.58.210.142 = 14 numbers and 3 numbers left to complete
Now simply add NUL after this IP address until you get total of 17 number-letters (numbers+NUL). This is how I create my NUL:
And it returns (
00 =
NUL):
In case your IP address has more than 17 numbers, remove the possibles NUL.