One important question that I'm unclear on is how long it takes to fix one of these cables. If it takes months then that is quite a wide window in which an attacker could incrementally take down cables.

Shhh, or somebody will realize how much slack there is in the system (for very good reasons, as evidenced here) and "optimize" it away...

Can anyone explain why there wasn't any BGP activity on the Finland-Germany systems when the cable broke, while for Lithuania there was a massive spike?

Unfortunately it's been a long time since I learned about BGP, if anyone could help out here I'd be grateful.

Exactly what the internet was built for!

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