Hi James, I just wanted to clarify a few points about how the probes work in response to your comment. All RIPE Atlas probes, even those not marked “public”, are available to be used in both built-in and user-defined measurements *as sources*. Many probes are not hosted on the open Internet, so they make for lousy targets. In most cases, they're hosted on internal networks, so they're often not “targetable” at all. More importantly, hosting a probe does not make your network (which already exists on the open Internet) any more or less likely to be the target of a measurement. And in terms of outgoing traffic, the probe generates next to nothing (typically a few Kb/s, even when it’s being used for user-defined measurements). You can learn more about this from the FAQs: https://atlas.ripe.net/about/faq/ Please let us know if you have any other questions. Regards, Daniel Quinn