Refer to the exhibit． S0/0 on R1 is configured as a multipoint interface to communicate with R2 and R3 in this hub-and-spoke Frame Relay topology． While testing this configuration, a technician notes that pings are successful from hosts on the 172．16．1．0/24 network to hosts on both the 172．16．2．0/25 and 172．16．2．128/25 networks． However, pings between hosts on the 172．16．2．0/25 and 172．16．2．128/25 networks are not successful． What could explain this connectivity problem?