A and B are connected via the same multi-access media. It is technically possible for B to tell A "you can reach 172.16.16.0/24 on the same media that you receive this update on". However what people seem to be saying is that there is no dynamic routing protocol that implements this.
Nope, you need to have IP route for it. If you choose not to tell the second router that it can do it, it would never even try. Repeat after me "My router does not call ms. Cleo to find out what I want. Router follows my instructions to the letter. I forgot to tell my router to do something. It therefore refused to do that something. I shall tell my router to do what I want it to do. It will follow my direct instruction." Now either configure a secondary IP on the second router, or create IP route pointing to the router that knows how to get to the destination. Alex