I recently upgraded to Red Hat 7 from 6 and noticed an issue where my /etc/resolv.conf file kept getting over written by network manager after every reboot. Specifically the search domain I set would be over written by something assigned by the dynamic dns server.
To stop this behavior you can edit /etc/NetworkManager/NetworkManager.conf and add the following parameter.
dns=none
This will stop the search domain from being altered across future reboots.
My full /etc/NetworkManager/NetworkManager.conf looks like so:
[main]
plugins=ifcfg-rh
dns=none