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Maximum length of the textual representation of an IPv6 address?
What would you recommend as the maximum size for a database column storing client ip addresses? I have it set to 16 right now, but could I get an ip address that is longer than that with IPv6, etc?
For IPv4, you could get away with storing the 4 raw bytes of the IP address (each of the numbers between the periods in an IP address are 0-255, i.e., one byte). But then you would have to translate going in and out of the DB and that's messy.
IPv6 addresses are 128 bits (as opposed to 32 bits of IPv4 addresses). They are usually written as 8 groups of 4 hex digits separated by colons: 2001:0db8:85a3:0000:0000:8a2e:0370:7334. 39 characters is appropriate to store IPv6 addresses in this format.
Edit: However, there is a caveat, see @Deepak's answer for details about IPv4-mapped IPv6 addresses. (The correct maximum IPv6 string length is 45 characters.)
If you want to handle IPV6 in standard notation there are 8 groups of 4 hex digits:
2001:0dc5:72a3:0000:0000:802e:3370:73E4
32 hex digits + 7 separators = 39 characters.
CAUTION: If you also want to hold IPV4 addresses mapped as IPV6 addresses, use 45 characters as @Deepak suggests.
Take it from someone who has tried it all three ways... just use a varchar(39)
The slightly less efficient storage far outweighs any benefit of having to convert it on insert/update and format it when showing it anywhere.
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.
IPv4 uses 32 bits, in the form of:
255.255.255.255
I suppose it depends on your datatype, whether you're just storing as a string with a CHAR type or if you're using a numerical type.
IPv6 uses 128 bits. You won't have IPs longer than that unless you're including other information with them.
IPv6 is grouped into sets of 4 hex digits seperated by colons, like (from wikipedia):
2001:0db8:85a3:0000:0000:8a2e:0370:7334
You're safe storing it as a 39-character long string, should you wish to do that. There are other shorthand ways to write addresses as well though. Sets of zeros can be truncated to a single 0, or sets of zeroes can be hidden completely by a double colon.