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From the database perspective, opening it up for access over LAN is the same as accessing it from anywhere, including the Internet. If you have a server at home for example, and you would like to reach it from work, all you have to do is setup the database to be accessible on your home LAN. To access your home LAN from work is a network setting, not related to the database configuration, that’s why you will not find any howto about it in any database tutorials.
Let me just point out that allowing direct access to the database from the Internet is a very, very bad idea, you’ll have your database cracked in no time. You could set up a VPN to access your system remotely in a secure way. To do so, you can refer to our openVPN setup guide.