For point to point in framerelay we create subinterfaces with different subnets, is there any necessory to create subinterfaces in point to multipoint ? if yes then why? i found in some books they created subinterfaces for point to multipoint but i didn't get why thay created?
waiting for your reply....
each point-to-multipoint subinterface equates an IP subnet.
The use of point-to-multipoint subinterface gives you the capability to mix different subinterface types and to have multiple point-to-multipoint subinterfaces mapping multiple IP subnets.
if you use directly the main interface it is true that it is point-to-multipoint with no additional configuration but it doesn't allow you to add other IP subnets.
In other words you may need to separate spoke routers in multiple groups each one with its own IP subnets associated with. This can be done to avoid the costs of a mesh between all spokes. It is more efficient to do in this way.
The use of point-to-multipoint subinterface allows to grow over time with no need to change existing configurations
I would never use on FR or ATM the main interface for this reason is always better to use a subinterface.
Hope to help