I have two networks: 192.168.13.0/24 (blue) and 192.168.15.0/24 (green).
Computer A is connected to the 13-net, only. Computer B has two interfaces, one in each network.
There is third computer that acts like a router and connects the 13-net to the 15-net (only in this direction).

Now, I'd like to ping 192.168.15.100 from computer A to B. Unfortunately there is never a reply. But when I use a hub instead of a switch it works.

In my opinion the ping packet travels through the switch to the router (which is the default route/gateway for A). The router sends the packet back to the switch to B. Probably B receives it on its 15-net interface but answers with it's 15th interface? Is this possible?
The problem is, that B may have only a gateway 192.168.13.50 - but I am not really sure of it (B is a embedded system with limited configuration possibilities).

Can anyone explain what happens here? Thank you!