Comment 398 for bug 417757

I disagree with making getaddrinfo() consider a host with only IPv6 link-local addresses to not have IPv6 connectivity. It does, it has IPv6 connectivity to all other IPv6 hosts on the directly attached links which also all have link-local addresses. This is actually the point of hosts automatically configuring link-local addresses on all interfaces all the time, and the IPv6 Addressing Architecture specifying that all interfaces must have link-local addresses - so that they can at a minimum always reach their on-link neighbors via link-local addressing. This is also why protocols such as IPv6 neighbor discovery, Multicast Listener Discovery and routing protocols such as OSPF use link-local addresses as source and/or destination addresses to reach their neighbors.

Combine autoconfigured IPv6 link-local addresses with a service discovery protocol such as Multicast DNS or SSDP, and you have Zero Configuration networking without any user intervention. Compare that with IPv4, where support for 169.254.0.0/16 is patchy, because it is done in userspace via DHCPv4. IPv6 will universally and reliably provide zero configuration networking.

I think it is reasonable to hosts more robust against broken devices in the network, but ignoring IPv6 link-local connectivity and then suppressing AAAA queries is not the solution. Happy Eyeballs (RFC6555) and IPv6 source and destination selection (RFC6724) are.