Randomly no connection to internet websites but could ping urls works.

Hi guys.
I know there are some thread similar, but this one is different and very strange.

Randomly, once or twice a day, for about one to 5 minutes, we are loosing connection to internet.
Right after that time every thing go back to normal again.

Few thing to noticed:

1. We still can ping Urls

2. DNS seems to work.

3. Accessing URL which are in the DMZ doesn't work as well.

4. I'm not sure if there are more fore shorter time, but this what i know of from my customers.


Any help will be appreciate.