RIP with discontiguous subnets

RIP(v1) routing is classful. This means the subnet mask is not sent along with routing updates, but rather assumed simply by the class of the subnet. Eg. 10.5.45.0 255.255.255.0 is advertised as a class A network, or 10.0.0.0/8. 192.168.9.0 is advertised as a class C and is advertised as 192.168.9.0/24.
So what if, as described in the below diagram, There are two different subnets being advertised that are not contiguous. Router A and C both know about separate 172.168 networks. The middle router will see identical route advertisements from both sides.



How do you resolve this? Well, use RIPv2, EIGRP, OSPF, or IS-IS (and don't summarize either of the 172.168 routes). This situation is just one of the reasons why classful routing is not used much any more, but watch out for a question like this on a CCNA test.