Looks like I managed to resolved issue. I am pretty new to linux command, so I ask my co-worker how to add dns entry on my ubuntu lts. So he gave me commands below.
vi /etc/network/interfaces
then go to the end of the line gateway, type a, then hit enter.
type dns-nameservers ipaddressofdns
then hit ESC
then :wq
then /etc/init.d/networking restart
My fogserver is faster than ever.