10.3.1. Handling Broken IPv6

One problem in practice that has been recently observed occurs when a host has IPv4 connectivity to the Internet but has "broken" IPv6 connectivity to the Internet in that it has a global IPv6 address but is disconnected from the IPv6 Internet. Since the default policy table prefers IPv6, this can result in unwanted timeouts.

This can be solved by configuring the table to prefer IPv4 as shown above. An implementation that has some means to detect that it is not connected to the IPv6 Internet MAY do this automatically. An implementation could instead treat it as part of its implementation of Rule 1 (avoid unusable destinations).