Squid 3.1 introduced
dns_v4_first option to query and use DNS A records first instead of AAAA records. This helped a lot in situations where IPv6 was “second-class citizen” compared to native IPv4 — that is: 6to4, 6in4 or otherwise tunneled.
Squid 5.0.4 marked
dns_v4_first as obsolete, according to changelog, but in fact removed the option at all, showing it as “ERROR” and making no effect. The documentation does not give any clue what other options supersede this one, nor does it provide any workaround.
I wonder if where is a new way to achieve the same functionality, perhaps using some new or good old directives, or by a combination of DNS (BIND) and Squid settings? Stop using IPv6 at all is of course an option, too, but not quite desired, much like reverting to al older Squid version.