[CentOS] Forcing IPv4 DNS lookups first before IPv6

Mon Apr 4 22:34:12 UTC 2011
Tom H <tomh0665 at gmail.com>

On Mon, Apr 4, 2011 at 10:51 AM, Russell Jones <rjones at eggycrew.com> wrote:
> I am having a strange issue with CentOS 5.4 that I cannot seem to solve.
> Every DNS lookup results in AAAA records being requested first before A
> records. As a result, this causes a large amount of unnecessary DNS
> traffic on the network. IPv6 has been completely disabled on these servers:
> /etc/modprobe.conf, ipv6 off and net-pf-10 off
> /etc/sysconfig/network, NETWORKING_IPV6=no
> lsmod | grep ipv6 shows the kernel module no longer loaded.
> Yet watching TCP dump shows that AAAA records are requested before A
> records every time a login is requested from one of our local machines
> to another. Is there some sort of configuration directive I can use to
> force IPv4 lookups first before IPv6? Or even better, stop IPv6 lookups
> all together?

Disabling ipv6 transport cannot prevent applications from making ipv6
queries - short of recompiling them as ipv4-only applications or
having applications check whether there is a non-link-local ipv6
address before making an ipv6 query. I've seen these checks discussed
but I don't think that they've been implemented - or, if they've been
implemented, backported to CentOS 5. It's been going on for a while: