network services may be slow (sendmail, CUPS etc) because default nameserver for the router always takes long time to resolve. To overcome this problem you have to load caching-nameserver, so does not have to do resolution every time.
yum install caching-nameserver
in system-config-network change DNS to 127.0.0.1
make sure to restart named:
service named restart
chkconfig named on
Just in case restart slow services (eg sendmail & cups)