An issue we've been seeing lately is a long delay in starting up the network interfaces resulting in no connectivity for the first 5 minutes or so after a reboot. The delay is caused by the bind9 (DNS) service and we have found that removing that from the startup sequence fixes this problem. If you are not utilizing the bind9 service you may remove it with the following command (this command is for Debian/Ubuntu and it will be different for other OSes but we have not seen this problem in other OSes):
rm /etc/network/if-up.d/bind9
Once removed, restart the networking service using this command: service networking restart
