I want to store the data returned by $_SERVER["REMOTE_ADDR"]
in PHP into a DB field, pretty simple task, really. The problem is that I can't find any proper information about the maximum length of the textual representation of an IPv6 address, which is what a webserver provides through $_SERVER["REMOTE_ADDR"]
.
I'm not interested in converting the textual representation into the 128 bits the address is usually encoded in, I just want to know how many characters maximum are needed to store any IPv6 address returned by $_SERVER["REMOTE_ADDR"]
.
IPv6 uses 128-bit (2128) addresses, allowing 3.4 x 1038 unique IP addresses. This is equal to 340 trillion trillion trillion IP addresses. IPv6 is written in hexadecimal notation, separated into 8 groups of 16 bits by the colons, thus (8 x 16 = 128) bits in total.
An IPv6 address is 128 bits in length and consists of eight, 16-bit fields, with each field bounded by a colon. Each field must contain a hexadecimal number, in contrast to the dotted-decimal notation of IPv4 addresses.
In hexadecimal, 4 bits (also known as ”nibble”) are represented by a digit or character from 0-9 and a-f (10-15). This format reduces the length of the IPv6 address to 32 characters.
An IPv6 address is represented as eight groups of four hexadecimal digits, each group representing 16 bits The groups are separated by colons (:). An example of an IPv6 address is: 2001:0db8:85a3:0000:0000:8a2e:0370:7334.
45 characters.
You might expect an address to be
0000:0000:0000:0000:0000:0000:0000:0000
8 * 4 + 7 = 39
8 groups of 4 digits with 7 :
between them.
But if you have an IPv4-mapped IPv6 address, the last two groups can be written in base 10 separated by .
, eg. [::ffff:192.168.100.228]
. Written out fully:
0000:0000:0000:0000:0000:ffff:192.168.100.228
(6 * 4 + 5) + 1 + (4 * 3 + 3) = 29 + 1 + 15 = 45
Note, this is an input/display convention - it's still a 128 bit address and for storage it would probably be best to standardise on the raw colon separated format, i.e. [0000:0000:0000:0000:0000:ffff:c0a8:64e4]
for the address above.
On Linux, see constant INET6_ADDRSTRLEN
(include <arpa/inet.h>
, see man inet_ntop
). On my system (header "in.h"):
#define INET6_ADDRSTRLEN 46
The last character is for terminating NULL, as I belive, so the max length is 45, as other answers.
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