How reliable is using IPv6 for unique user identification in PHP sessions?

Using IPv6 for unique user identification in PHP sessions can be reliable, as IPv6 addresses are typically unique for each device. However, it's important to consider that some users may have dynamic IPs or be behind a proxy server, which could affect the uniqueness of the identifier. To enhance reliability, you can combine the IPv6 address with additional user information, such as a user agent or a randomly generated token. 

$ipv6 = $_SERVER['REMOTE_ADDR'];
$user_agent = $_SERVER['HTTP_USER_AGENT'];
$unique_id = md5($ipv6 . $user_agent);

session_id($unique_id);
session_start();

Keywords

IPv6 unique user identification PHP sessions reliability security.

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