Max length for client ip address

Question

Possible Duplicate    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

User · Accepted Answer

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

User · Answer

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

User · Answer

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

User · Answer

If you are just storing it for reference  you can store it as a string  but if you want to do a lookup  for example  to see if the IP address is in some table  you need a  canonical representation    Converting the entire thing to a  large  number is the right thing to do   IPv4 addresses can be stored as a long int  32 bits  but you need a 128 bit number to store an IPv6 address   For example  all these strings are really the same IP address  127 0 0 1  127 000 000 001    1  0 0 0 0 0 0 0 1

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

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