I have a BearExtender n3 that I use to access weak (or far away) wifi networks. When I’m using it I usually share my Internet connection through Airport.

Except this stopped working after I upgraded to Snow Leopard.

After Googling for eons, I finally came across a fix. Though it was advertised for connecting a Squeezebox or Xbox 360, it works just as well for MacBooks and iPhones.

Start Internet Sharing
This will create a file called “bootpd.plist” in /etc. Copy this file to your desktop.¹

Stop Internet Sharing
Open “bootpd.plist” in a text editor. Look for a key called “reply_threshold_seconds” near the bottom of the file. It should have an integer value of 4. Change this value to 0 and copy the file back to /etc.

When you restart Internet Sharing everything should work again.²

1. To get to /etc, open a new Finder window, type command-shift-g and enter “/etc” in the text field. ↩
2. If it still doesn’t work, check “bootpd.plist” in /etc and make sure “reply_threshold_seconds” is still set to 0. ↩