You have two possibilities (for an IPv4 address) :
a varchar(15), if your want to store the IP address as a string
192.128.0.15 for instance
an integer (4 bytes), if you convert the IP address to an integer
3229614095 for the IP I used before
The second solution will require less space in the database, and is probably a better choice, even if it implies a bit of manipulations when storing and retrieving the data (converting it from/to a string).
For IPv4 addresses, you can use VARCHAR to store them as strings, but also look into storing them as long integesrs INT(11) UNSIGNED. You can use MySQL's INET_ATON() function to convert them to integer representation. The benefit of this is it allows you to do easy comparisons on them, like BETWEEN queries