iMac OSX Lion loses internet connection (ethernet) waking up from sleep

My brand new iMac running Mac OS X 10.7.3 loses internet connection after computer wakes up from sleep. This is not a WiFi problem because I am plugged in with ethernet. It loses its connection roughly 50% of the time it wakes up and then I have to go through the diagnostics and reboot my cable modem and router. It is very frustrating. I have tried renewing the DHCP lease but the problem continues. Has anyone encountered this problem and what did you do to fix it? Thanks in advance.