This plugin adds to your Matomo installation a new dimension called visit_subnetwork then reports visitor counts coming from private networks.
Configure settings by Matomo's administration page. You can choose to include common private subnetwork, such as 127.x.x.x, 192.x.x.x and 10.x.x.x.
You can also configure your custom subnet rule by writing a regular expression.
This plugin is a complete refactoring working on Matomo 3.x of original IntranetSubnetwork was published for Piwik 2.x.
View and download this plugin for a specific Matomo version: