It's also trivial to roll your own version of dropbox. With IPv6 it's possible to fail to configure those nftables rules. The firewall could be turned off.
In theory you could turn off IPv4 NAT as well but in practice most ISPs will only give you a single address. That makes it functionally impossible to misconfigure. I inadvertently plugged the WAN cable directly into my LAN one time and my ISP's DHCP server promptly banned my ONT entirely.
In theory you could turn off IPv4 NAT as well but in practice most ISPs will only give you a single address. That makes it functionally impossible to misconfigure. I inadvertently plugged the WAN cable directly into my LAN one time and my ISP's DHCP server promptly banned my ONT entirely.