On the IP host model

Yesterday's discovery at work is a little-known aspect of IP known as the weak and strong host model. Roughly speaking, in the weak host model a system behaves as if all of its assigned IP addresses are available on all interfaces, while in the strong host model a system behaves as if each of its assigned IP addresses belongs to a specific interface.

Linux uses the weak host model, with apparently no way to control this.

This, combined with a somewhat complicated network setup, lead to a weird situation where two boxes can ping each other, have full access to other networks, but cannot create a TCP connection between each other.

( Complicated networking details )