This is a simple PHP script I wrote for detecting whether a visitor to a page is connected via IPv4 or IPv6, matching the remote address server variable or an address passed as a query parameter to a regular expression and returning the address and protocol as JSON.
I found the IPv6 regular expression through a Google search; and yes, I know it doesn’t check to see if the address is valid. No need for that, I say, when it’ll mostly be using server-side values for the visitor’s address. A basic implementation using jQuery (replacing, of course, the URL of the script with wherever you choose to host it) would look something like this:
<span id="remote_ip" /> or
<div id="remote_ip" /> (remember the
/, or closing tag to stay HTML5-valid) would be replaced with
Connected via IPv6 from 2000:4000:aaa:22bb::dead:b33f
so that a visitor can see what protocol and address they’re connected with. You can also use the script to track how many visitors to your site use IPv6. It may be trivial, but it’s just something I threw together on a whim because I felt like it and thought it’d be a fun exercise in regular expressions, JSON, and jQuery.