Get IP address and add it to the Google Tag Manager data layer. Uses the free ipify.org service and intelligent caching to minimize requests.

gtm-ipify.html

<script>

  /*
   * get ip address and add it to the GTM data layer
   * uses the free ipify.org service
   * and intelligent caching to minimize requests
   */

  // mark the start of the script loading
  window.dataLayer = window.dataLayer || [];
  window.dataLayer.push({
    "event": "ipify.js",
    "ipify.start": (new Date()).getTime()
  });

  (function () {

    "use strict";

    var ip, newNode, referenceNode;

    // helper function to execute once we have the IP address
    function putIPinDataLayer (ip) {

      window.dataLayer.push({
        "event": "ipify.load",
        "ipify.ip": ip
      });

    }

    if (sessionStorage) {
      ip = sessionStorage.getItem("ipify.ip");
    }
    if (ip) {

      // use IP address retrieved from session cache
      putIPinDataLayer(ip);

    } else {

      // use ipify.org to get IP address
      // listen for when the IP address has been loaded by ipfiy
      window.ipifyCallback = function ipifyCallback (json) {

        if (sessionStorage) {
          sessionStorage.setItem("ipify.ip", json.ip);
        }
        putIPinDataLayer(json.ip);

      };

      // inject the script from ipify.org
      newNode = document.createElement("script");
      newNode.async = true;
      newNode.src = "https://api.ipify.org?format=jsonp&callback=ipifyCallback";
      referenceNode = document.getElementsByTagName("script")[0];
      referenceNode.parentNode.insertBefore(newNode, referenceNode);

    }

  }());

</script>