In the Providers report, what does “Unknown” mean?

Matomo (Piwik) uses a special php function (gethostbyaddr) to request the hostname associated to a given IP. For example, the function would return “br76.comcast.net” and Matomo would categorize the visitor as using the provider “Comcast”. Sometimes however, for specific IPs or when the function times out, Matomo doesn’t know which provider the visitor is using and will simply report “Unknown”.