The other day one of our internal DNS needed to be shut down for maintenance. During that time people complained about slow responsiveness of the applications running on our RHEL machines. Because the DNS maintenance was the only change we made at that time we started looking in that direction.
As it turned out, it seems that Linux is trying to contact the first DNS server in the resolv.conf file for every DNS query. The second one is queried after x number of seconds
I added the following options to /etc/resolv.conf to make better use of the second nameserver in the list.