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"].
This question is related to
ip
ip-address
ipv6
I think @Deepak answer in this link is more close to correct answer. Max length for client ip address. So correct size is 45 not 39. Sometimes we try to scrounge in fields size but it seems to better if we prepare enough storage size.
As indicated a standard ipv6 address is at most 45 chars, but an ipv6 address can also include an ending % followed by a "scope" or "zone" string, which has no fixed length but is generally a small positive integer or a network interface name, so in reality it can be bigger than 45 characters. Network interface names are typically "eth0", "eth1", "wlan0", so choosing 50 as the limit is likely good enough.
Watch out for certain headers such as HTTP_X_FORWARDED_FOR that appear to contain a single IP address. They may actually contain multiple addresses (a chain of proxies I assume).
They will appear to be comma delimited - and can be a lot longer than 45 characters total - so check before storing in DB.
Answered my own question:
IPv6 addresses are normally written as eight groups of four hexadecimal digits, where each group is separated by a colon (:).
So that's 39 characters max.
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.
Source: Stackoverflow.com