As described in the IPv6 Wikipedia article,
IPv6 addresses are normally written as
eight groups of four hexadecimal
digits, where each group is separated
by a colon (:)
A typical IPv6 address:
2001:0db8:85a3:0000:0000:8a2e:0370:7334
This is 39 characters long. IPv6 addresses are 128 bits long, so you could conceivably use a binary(16) column, but I think I'd stick with an alphanumeric representation.
