Refer to the exhibit. S0/0 on R1 is configured as a multipoint interface to communicate with R2 and R3 in the hub-and-spoke Frame Relay topology. While testing this configuration, a technician notes that pings are successfully from hosts on the 172.16.1.0/24 network to hosts on both the 172.16.2.0/25 and 172.16.0.2.128/25 networks. However, pings between hosts on the 172.16.2.0/25 and 172.16.2.128/25 network are not successful.
What could explain this connectivity problem?
A.
The ip subnet-zero command has been issued on the R1 router.
B.
The RIPv2 dynamic routing protocol cannot be used across a Frame Relay network.
C.
Split horizon is preventing R2 from learning about the R3 networks and R3 from learning about R2 networks.
D.
The 172.16.2.0/25 and 172.16.2.128/25 networks are overlapping networks that can be seen by R1, but not between R2 and R3.
E.
The 172.16.3.0/29 network used on the Frame Relay links is creating a discontiguous network between the R2 and R3 router subnetworks.
Under normal circumstances, the router that is connected to the broadcast IP network and uses the distance vector routing protocol will use split horizon mechanism to avoid routing loop.
Split horizon is a technology to avoid routing loop and speed up the routing convergence. The router may receive the routing information sent by itself which is useless, split horizon will not advertise the routing update information back received from the terminal, while it will advertise those routes that will not be cleared because of the endless counting .It can be simply interpreted that the route learnt by a router from one interface will not be sent through the same interface .
For the non-broadcast network (such as Frame -Relay and High Speed Switched Data Services), the effect of split horizon is not ideal. So, we can use the following commands to disable or enable split horizon, ip split-horizon to enable split horizon
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