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Should I use protocol-relative URLs in ad tags?

Ad tags can be placed in many areas of a website: some secure areas and some non-secure areas. However, non-secure content can be blocked by the browser when the web page is secure. The error message in Internet Explorer is "This Page Contains Both Secure and Non-Secure Items. Do you want to display the nonsecure items?" Other browsers can simply ignore and skip the non-secure content. This means a non-secure ad might not display within a secure website. This is one of the common sources for data discrepancy if there are multiple ad servers involved in tracking the same ad impression.

Therefore, it's better to use the same protocol for all URL requests, either all "http://" or all "https://". For ad serving, it means using the secure ad serving tag on secure sites and the non-secure ad serving tag on non-secure sites. To do this, you can manually match the correct ad tag with your website's area. For example: a non-secure ad tag for the homepage and a secure ad tag for the login area. However, there is a better and more convenient way by using protocol-relative URLs. It is also called scheme-relative URLs or network-path references.

Instead of using this ad serving tag for non-secure web pages:
<iframe src="http://g.adspeed.net/ad.php...">
<a href="http://g.adspeed.net/ad.php..."><img src="http://g.adspeed.net/ad.php..."/></a>
</iframe>
or this ad serving tag for secure web pages:
<iframe src="https://g.adspeed.net/ad.php...">
<a href="https://g.adspeed.net/ad.php..."><img src="https://g.adspeed.net/ad.php..."/></a>
</iframe>
You can use a protocol-relative URL that has auto-detection and auto-switching:
<iframe src="//g.adspeed.net/ad.php...">
<a href="//g.adspeed.net/ad.php..."><img src="//g.adspeed.net/ad.php..."/></a>
</iframe>

Considerations

This setup can be applied to other URLs, not just our ad serving tags. However, there are several considerations you need to know before you convert all URLs to this format:
  • The SSL certificate needs to be valid and working for the same domain as the non-secure/standard domain. If you have SSL on a different domain or sub-domains then this scheme will not work. For example: http://client.example.com and https://client.example.com
  • Really old browsers might not support, understand or properly handle this protocol-relative URL format. Potential issues with these older browsers include double-download of the same file and missing file error
  • Some email software converts protocol-relative URLs to "file://" URLs and try to look in a folder on the client's computer, which likely does not exist. This also happens when you view the web page locally after downloading it.

Other Articles in Ad Tag

This section describes the ad tag (serving code) with basic and advanced settings. It includes common ad serving setup instructions and answers frequently asked questions when integrating the ad tag into your site, blog or app.

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