What is the crossdomain.xml file?

What is the crossdomain.xml file?

The crossdomain.xml file is a cross-domain policy file. It grants the Flash Player permission to talk to servers other than the one it's hosted on.

In what circumstances do I need to use one?

You need a crossdomain.xml file when your Speedtest uses external hosts as testing servers.

• the Speedtest application is hosted on your main webserver (www.mycompany.com for example), but you have a dedicated testing server that the test uses. (speedtest.mycompany.com)
• You want to use more than 2 threads. You will need a crossdomain file to allow access to speedtest2.mycompany.com
• You have multiple servers

What should it look like?

If your company's website is hosted at www.mycompany.com and you also wanted to allow speedtest.net to use your server as a host, your crossdomain would look like:

<?xml version="1.0"?>
<cross-domain-policy>
    <allow-access-from domain="*.mycompany.com" />
    <allow-access-from domain="*.speedtest.net" />
</cross-domain-policy>

This file goes in  the root of document folder on the server you want to allow access. Ex: http://speedtest.mycompany.com/crossdomain.xml in this case.

url:(https://support.ookla.com/entries/21097566-what-is-crossdomain-xml-and-why-do-i-need-it)

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