`git blame` is your friend sysctl.d: switch net.ipv4.conf.all.rp_filter from 1 to 2 This switches the RFC3704 Reverse Path filtering from Strict mode to Loose

`git blame` is your friend sysctl.d: switch net.ipv4.conf.all.rp_filter from 1 to 2 This switches the RFC3704 Reverse Path filtering from Strict mode to Loose mode. 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). 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. The distributions that don't care about the client use cases and prefer a strict filter could just ship a custom configuration in /usr/lib/sysctl.d/ to override this. https://github.com/systemd/systemd/commit/230450d4e4f1f5fc9fa4295ed9185eea5b6ea16e https://github.com/systemd/systemd/commit/230450d4e4f1f5fc9f... There was NEWS entry for this here: https://github.com/systemd/systemd/blob/230450d4e4f1f5fc9fa4295ed9185eea5b6ea16e/NEWS#L73-L80 https://github.com/systemd/systemd/blob/230450d4e4f1f5fc9fa4... as to _why_ they would make the change? Systemd trieds to be project for distros to have a sane base system. Introducing this change was probably something they deemed as being useful in a base system. Especially in the context of laptops and mobile devices this default seems sane.