We try to null-route (plainly block) attacks, preventing servers from being drowned in traffic so that other LFS services remain available, which is why you could still ping it. But by blocking the attacks (closing ports), we do block the service behind it as well, which is why the master is / was down from time to time.
The websites now sit behind CloudFlare and the web server has been locked down with switch ACL's. This already has protected the website from attacks late last night.
The website indeed has always been available through IPv6 because the attack only occurred on IPv4.
Finally, we have a plan to better protect the master, however it will take a bit of work and a patch for LFS. Hopefully that will come later this week.