Previously, when using multiple subnets on an external network, traffic from one subnet to the other would be forwarded through the upstream router first.
This resulted in massive inefficiency, to the point that adoption of the concept of multiple subnets on an external network was hindered.
This update addresses this issue by adding an on-link route to each subnet.
As a result, a router connected to an external network is attached to one subnet, thus having one IP address (even if that network has multiple subnets). With this fix, the router will still consume an IP address from only subnet, but also has an on-link route to all subnets on the network.