It's clear from this forum that the cause of loss of internet connection is different for different people. This forum originally started as a loss of ethernet connection but has more recently included loss of wifi connections as well.
I have tried every single thing suggested in this forum to try to connect via ethernet after sleep and every single thing has failed. I have deleted recommended prefs, changed to manual settings, deleted ethernet and re-added ethernet to system preferences, deleted logs and caches, altered energy savings settings, tried new ethernet cables, connected directly to the modem, switched ports on both the modem and the router, zapped the PRAM or whatever, unplugged the computer, restarted dozens of times, etc., etc., all to no avail. The loss of ethernet connection has gradually gotten worse and worse and, alas, will not connect AT ALL at this time. I have a three year old iMac with all the RAM it will hold, I use an Apple AirPort Extreme as my router and have no trouble connecting to the internet via it's WiFi. It connects first time, everytime on this iMac as do all other iPhone's, iPads, and iPods we have in the house. An old MacPro connects just fine through the same router via ethernet. As I posted previously, I had finally resolved to never sleep my mac because of this problem, but unfortunately you have to occasionally restart because of computer funkiness or software updates. In the past, I've been able to unplug/replug my ethernet cable a few times and it would finally activate it's connection, but this no longer works, even with a new ethernet cable. This problem has been going on now for two years, starting just shortly after my warranty ran out. I am so discouraged by my experience with this iMac (which I didn't really want in the first place; I'd always had MacPros over the past 20 plus years), that I was hoping Windows 8 might offer a legitimate option. I believe this problem to be hardware related in my case, since I've rulled out the modem, the router, and since it would connect by manually unplugging and replugging the ethernet cable in the past. At least I can still connect to the internet by WiFi, but, looking at this forum, who knows how much longer that will last!