Max length for client ip address [duplicate]

Answer 1

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.

Answer 2

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.)

Answer 3

People are talking about characters when one can compress an IP address into raw data.

So in principle, since we only use IPv4 (32bit) or IPv6 (128bit), that means you need at most 128 bits of space, or 128/8 = 16 bytes!

Which is much less than the suggested 39 bytes (assuming charset is ascii).

That said, you will have to decode and encode the IP address into/from the raw data, which in itself is a trivial thing to do (I've done it before, see PHP's ip2long() for 32-bit IPs).

Edit: inet_pton (and its opposite, inet_ntop()) does what you need, and works with both address types. But beware, on Windows it's available since PHP 5.3.

Answer 4

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.

Answer 5

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.

Answer 6

There's a caveat with the general 39 character IPv6 structure. For IPv4 mapped IPv6 addresses, the string can be longer (than 39 characters). An example to show this:

IPv6 (39 characters) :

ABCD:ABCD:ABCD:ABCD:ABCD:ABCD:ABCD:ABCD

IPv4-mapped IPv6 (45 characters) :

ABCD:ABCD:ABCD:ABCD:ABCD:ABCD:192.168.158.190

Note: the last 32-bits (that correspond to IPv4 address) can need up to 15 characters (as IPv4 uses 4 groups of 1 byte and is formatted as 4 decimal numbers in the range 0-255 separated by dots (the . character), so the maximum is DDD.DDD.DDD.DDD).

The correct maximum IPv6 string length, therefore, is 45.

This was actually a quiz question in an IPv6 training I attended. (We all answered 39!)