Visiting a friend this weekend, and he mentioned network weirdness since switching to a new ISP. His printer would spew pages in the night. In the morning his laptop was running because it received a WoL packet, and so on.

I guessed his IPv6 packet filter was not, offered to look.

His ISP-provided "firewall" was an IPv4 NAT and an IPv6 router. No packet filtering by default, but the management app allowed creating rules to block outbound access from specific devices.

So, if you're seeing weirdness from your devices, your ISP's gear might be leaving you naked on the IPv6 Internet.

Also: IPv4 NAT is not a firewall.