It’s worth paying attention to how these networks are put together and managed as our government seeks to surrender control of the internet’s backbone.

A number of popular websites like Twitter and Netflix went down for some users on Friday in a massive cyberattack with international reach.

Affected sites included Twitter (TWTR, Tech30), Etsy (ETSY), Github, Vox, Spotify, Airbnb, Netflix(NFLX, Tech30) and Reddit.

Dyn, which manages website domains and routes internet traffic, experienced two distributed denial of service attacks on its DNS servers. A DDoS attack is an attempt to flood a website with so much traffic that it impairs normal service.

“If you take out one of these DNS service providers, you can disrupt a large number of popular online services, which is exactly what we’re seeing today,” said Jeremiah Grossman, chief of security strategy at cybersecurity startup SentinelOne.

The massive outage drew the attention of the FBI which said Friday that it was “investigating all potential causes” of the attack.