I was doing the lab of ODR and my R1 is not configured as point-to-point. I expereinced that even though R5 can see it in "sh cdp neighbor" but R2, R3 and R4 are unable to ping R1 Loopback.
While R5 can ping to R1 and all. and R1 can ping to all as well. After spending some time I just changed the R1 multipoint interface to point-to-point and than everthing start working fine.
I need to know why this happen it means that the stub should always be point-to-point. (R5 is a HUB)