I have a small network managed network that about every three days at least one computer will not resolve DNS. It can be the same computer, but the problem typically happens between three or four different machines. I can ping my default gateway, ping numerical IP address, but not yahoo.com for instance. The Internet broswer fails to load any web pages. Then maybe 20 minutes to 2 hours the problem is gone and they problem computer is functioning normally. There are no error messages at the command line when the ping fails? Any help appreciated.