[CentOS] Forcing IPv4 DNS lookups first before IPv6

[Adam Tauno Williams]

On Mon, 2011-04-04 at 09:51 -0500, Russell Jones wrote:
> Hello!
> 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:

Doubtful, if you are seeing AAAA lookups.  Does "ip addr" show any IPv6
interfaces?

> /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

You *only* sees these for login?  Perhaps some authentication module you
are using is causing them to happen?

>  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?

I don't believe you see IPv6 lookups from the normal resolver libraries
unless there is at least one active IPv6 interface.