6to4 suddenly stopped working to 2001: addresses

I've got three installations of FreeBSD using 6to4 in three different physical locations, attached to three different ISPs. Sometime in the last few days all of them have stopped talking to IPv6 addesse which are not also 6to4. I can still talk to 2002: addresses, but not to 2001: addresses. This

Re: 6to4 suddenly stopped working to 2001: addresses

I've got three installations of FreeBSD using 6to4 in three different physical locations, attached to three different ISPs. Sometime in the last few days all of them have stopped talking to IPv6 addesse which are not also 6to4. I can still talk to 2002: addresses, but not to 2001: addresses.