The monkeys pounding keyboards to write consumer firewall software haven't stumbled on to a working IPv6 version yet. My AT&T router needs a strange set of firewall options to even marginally pass IPv6. I found those options by brute-force trial and error while watching packet captures. If I hadn't been in a good mood at the time, I might have thrown the router and a panicking Mac Mini Server into a wood chipper. Or used IPv4. Not sure, really.