Setting IPv4 as preferred protocol over IPv6

Solution 1:

According to the man page, inserting a precedence value in gai.conf disables the all the other default rules. Try setting all the rules as listed in RFC 3484 (10.3):

  Prefix        Precedence Label
  ::1/128               50     0
  ::/0                  40     1
  2002::/16             30     2
  ::/96                 20     3
  ::ffff:0:0/96        100     4

Solution 2:

ipv6 isn't really my area of expertise, but on the man page for resolver(5) there seems to be a few options in /etc/resolv.conf that could be related:

options inet6 sets RES_USE_INET6 in _res.options. This has the effect of trying a AAAA query before an A query inside the gethostbyname(3) function, and of mapping IPv4 responses in IPv6 "tunneled form" if no AAAA records are found but an A record set exists.

Maybe your clients have that option set?