Hello Ankur,
when a single IP subnet is used over a partial mesh FR topology the following occurs:
not all the hosts in the IP subnet can reach each other directly using a FR PVC (or it would be a full mesh).
This is quite a departure from how routing works normally: using a third device to reach a device in the same IP subnet is somewhat not expected.
This makes routing more difficult to implement, for example in the case of OSPF the choice of the DR becomes critical as only a device with direct connections to all other routers in subnet can do the job.
In real world a partial mesh can be mapped to a collection of point-to-point links each with its own IP subnet, making routing simpler with any routing protocol and specially with OSPF.
Hope to help
Giuseppe
