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 ».