add docs for https://github.com/opnsense/core/issues/3856

source/manual/aliases.rst

@@ -96,6 +96,34 @@ region.
   .. image:: images/firewall_geoip_alias.png
       :width: 100%
 
+To use GeoIP, you need to configure a source in the :menuselection:`Firewall --> Aliases -> GeoIP settings` tab, the most commonly
+used source is MaxMind, for which we have a how-to available : :doc:`how-tos/maxmind_geo_ip`
+
+The configured url should point to a zip file containing the following csv files:
+
+.. list-table:: Title
+   :widths: 50 25 25 25
+   :header-rows: 1
+
+   * - Filename
+     - Purpose
+     - Format
+     - Example
+   * - %prefix%-locations-en.csv
+     - maps geo locations to iso countries
+     - geoname_id,,,,country_iso_code
+     - 1,,,,NL
+   * - %prefix%-IPv4.csv
+     - IPv4 networks
+     - network,geoname_id
+     - 2.21.241.0/28,1
+   * - %prefix%-IPv6.csv
+     - IPv6 networks
+     - network,geoname_id
+     - 2001:470:1f15:210::/64,1
+
+The :code:`%prefix%` can be used to identify the product and/or vendor, in MaxMind's case these files are named
+:code:`GeoLite2-Country-Locations-en.csv`, :code:`GeoLite2-Country-Blocks-IPv4.csv`, :code:`GeoLite2-Country-Blocks-IPv6.csv` for example.
 
 .. Tip::
 

source/manual/how-tos/maxmind_geo_ip.rst

@@ -14,7 +14,7 @@ Goto https://www.maxmind.com/en/geolite2/signup and create your account. Note th
 Generate Licence Key
 ######################
 
-Once you have created an account you'll need to create a license key. Click in the "My Licence Key" link and generate a key. Save the key ID somewhere safe!!! 
+Once you have created an account you'll need to create a license key. Click in the "My Licence Key" link and generate a key. Save the key ID somewhere safe!!!
 
 You do not need to download the config at this point.
 
@@ -26,7 +26,7 @@ Now we need to create the link we'll need in OPNsense, all you need to do now is
 
 https://download.maxmind.com/app/geoip_download?edition_id=GeoLite2-Country-CSV&licence_key=My_Licence_key&suffix=zip
 
-You can check that you have done it correctly by just pasting the link into a browser, it should download the zip file. 
+You can check that you have done it correctly by just pasting the link into a browser, it should download the zip file.
 
 
 ##########
@@ -34,4 +34,3 @@ OPNsense
 ##########
 
 In OPNsense, goto Firewall:Aliases and select the GeoIP settings tab. Enter the URL you have created into the URL box and click Apply, and that's it.
-