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How to do this:
1) Log into the web management tool via port 5000 or 5001.
2) Go to Control Panel -> "Security" -> Select the "Firewall" Tab
3) Click Create. The "Create Firewall Rules" window will come up
4) Ports -> All
5) Source IP -> Subnet
6) IP Address: 18.0.0.0
7) Subnet Mask: 255.0.0.0
8) Action -> Allow
9) Click OK
10) Click on the "Save" button right under the tabs. If you forget to save like I often do, and try to leave the page, it will ask if tell you "Changes are not saved. Are you sure you want to leave without saving. ?" Click on no "No" and make sure you save the setting.
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1) At the bottom of the Control Panel -> Firewall window there should be a line that starts with “If no rules are matched”
2) Click on "Deny access”.
Again, remember to save. Fortunately if you attempt to navigate away or close the window without saving, it will let you know again that changes are not saved.