I should add that connections can be made between firewalled clients. But it would require the aid of a non-firewalled host service.

This is how services like Skype could still be usable by firewalled users. So long as the Skype service is hosted on non-firewalled host, the service can help negotiate connection between users.

I just noticed that I used the term 'cable' and it can also mean other things; I meant fiber-optic.

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Skulls! Multi-Network WebCache

I don't know, I never tried it directly at my home but I have seen friends with Fastweb.
The IPV4 IPs start with "10."
I don't know about IPV6.

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Skulls! Multi-Network WebCache