Also instructive is the commit message: > The Strict mode breaks some pretty common and reasonable use cases, such as keeping connections via one default route

Also instructive is the commit message: > The Strict mode breaks some pretty common and reasonable use cases, such as keeping connections via one default route alive after another one appears (e.g. plugging an Ethernet cable when connected via Wi-Fi). > The strict filter also makes it impossible for NetworkManager to do connectivity check on a newly arriving default route (it starts with a higher metric and is bumped lower if there's connectivity). And it goes on pointing out what you also mentioned about kernel defaults: > Kernel's default is 0 (no filter), but a Loose filter is good enough. The few use cases where a Strict mode could make sense can easily override this.