At times, our clients run their services in restricted networks, where they cannot have anyone from the public internet connect. This makes using our testing service a challenge, since by default, our service will allocate a machine on the cloud vendor we use and then dynamically be assigned an IP address.
By default, our service uses GCP for its probe machines. You can decide to open up the range of IP addresses that GCP publishes per region or for their whole network. As this may change from time to time, GCP has created an API for that: https://www.gstatic.com/ipranges/cloud.json
Oftentimes, our clients will open up their lab or network for our probes only when they conduct tests, closing it up again once done.