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I *think* this might be accomplished by using Access Control.Go to Advanced -> Access Control. Enable Access Control.Then click Add policy.Go through the wizard.When you get to Add Machine, you can add all PC's at once.Default is "Block some access".Click "Apply Advanced Port Filters".Give it a name, and keep the Dest IP address and End IP address default. Just change the port to 53. Then click Save.That should work for you. I can't test it myself due to me being at work.