From a purely technical perspective, what manner do you think Iran's cut off the internet outbound/inbound internet from the rest of the world?

Mods: If this is considered political, pls remove.

I didn't see any low-level explanations on how Iran was able to basically detach from the Internet and I'm curious if anyone had any thoughts.

My first guess is that they did not unplug inbound fiber and instead modified configurations (as the ISP's are government owned) to allow for government-only traffic.

Thoughts?