Mac OS X - Internet Sharing and bootpd.plist
Internet sharing on Mac OS X has proven to be nothing but problematic for me. I had tried time and time again to share my dorm connection from my Macbook Pro to my Xbox 360 and iPhone for online gaming and Spotify (which doesn’t seem to play nice on a 802.1x network). After exhausting all other solutions, I finally found one that worked.
To cut an overly excessive post short, connecting to my Macbook from an external device did not work manually. Believing this to be an error on my part, I found a guide to connect to my Macbook using Internet Sharing via DHCP. This did not go well as my bootpd.plist did not exist, after exhausting all options I decided it was time to bite the bullet and reformat OS X to a factory state.
After the reformat, and performing a full OS update I have finally been able to perform the subsequent stages of the walkthrough (linked above) and am now able to share my internet to any device. I recommend you make a clone of your hard drive prior to reformatting, as you can later use Migration Assistant to transfer back your applications and file system. If you do this however, it would probably be best not to migrate your system files, otherwise you could be back to square one.
I have used Mac OS X since early 2007. Since then I have not performed one reformat. My system has migrated several OS version since then, as well as applied many system updates. Until now everything has been tip top. I believe with proper maintenance, OS X should not need reformatting. I deem this case exceptional as I have read from several sources that Internet Sharing support has been dropped by Apple. As odd as this seems, this could explain how my reformat solved the problem.
Disclaimer: Follow my advice at your own risk. If you lose something after following this advice then it is your own fault. Always backup your system, especially prior to something drastic like a reformat.