I have a DLink DSL-2520u ADSL2+ modem. When I access the page
http://192.168.1.1/, it prompts for a username and password. Upon successful authentication, I see the modem configuration page.
If I am on a different network, I can also access the modems configuration via its public IP address.
How can I restrict access to the configuration page via the public IP address and only allow access via the internal IP address?