Facter version: 4.0.52
OS Ubuntu Linux 20.04
For gathering the networking fact, facter reads in the whole routing table (ip route show, ip -6 route show).
In facter 3 this happended once, in facter 4.x this happens once for every interface.
For router deployments, this makes a huge difference, as these both have potentially a huge routing table (a router with a BGP full table can easily have over 1 million routes) and 20 interfaces.