Here in the picture you can see a simple senario setup of 3 routers connected over Ethernet in a Hub and Spoke topology, simple solution for frame relay was to do point-to-point sub interfaces and connect them all, but as the CCIE Lab Exam is not a best practice lab they will usually ask you to work only on the physical interface and due to that you will be faced with a problem of split horizon rule where one update that will be received on the physical interface from R1 cannot be Sent out that same interface to R3 and due to that R3 will be left out of the picture as far as the updates (same goes for the other way around). so what is the solution well in that case and only in that case it will be safe to turn the Split Horizon on R2. and how you do it?
Example under R2 Serial Interface:
interface Serial 0/0
ip add 192.168.0.2 255.255.255.0
no ip split-horizon eigrp