Networks

Suppose we have two routers which are connected to each other, and then after that a switch connects two hosts. like this:

Computer X, Computer Y to switch0 to Router A to Router B to Switch1 : Computer A, Computer B

suppose we want to use the network 172.154.30.0 for the routers and assign the first usable address to Router A and the second one to Router B. which mask should we select in this case and why???