Using dhcp within a ifcfg network configuration file you may want to specify a different nameserver instead of using the nameserver assigned by the DHCP server.
Use the PEERDNS, DNS1 and DNS2 options.
DEVICE="ck" BOOTPROTO="dhcp" ONBOOT="yes" TYPE="Ethernet" PEERDNS="yes" DNS1="184.108.40.206" DNS2="220.127.116.11"
To check that it all works
grep ^nameserver /etc/resolv.conf
nameserver 18.104.22.168 nameserver 22.214.171.124
If you want to use the nameservers that are provided by DHCP server but also specify an extra nameserver within your
/etc/resolv.conf, you can make use of
dhclient.conf options in
prepend domain-name-servers 126.96.36.199;