IBGP + Prepend Default route

[John Levy]

Hello , so i got a school project and i would like to get some help guys.
Actually need more an expert-advise. 
This is my project - 

The mission is pretty simple , but i stuck on the default route.
Lets consider PC-1 As a remote customer that supposed to be able to ping the ISP.
THE ISP is the default route (works fine with default-originate)  TO R1 & R2.
I want to advertise for example to R3 that R1 its his default route and R2 should also be a defualt route but with a bigger AS PREPEND. (mean that if default route from R1 Will failed , only then Use R2 default route).

How can i do it ?

Another Question , if i want that all the traffic then return to the network (For Example from facebook.com to R4) it will be directed through R1 .  is this mission can be accomplished with LOCAL PREF from ISP ? 

Thank you !!!! 

[Harold Ritter]

Hi John,

It is not possible to use the AS path prepend feature on an iBGP session, as this would go against the BGP specifications. You can use AS prepend as you receive paths on R2 from the ISP.

As for the ingress traffic returning via R1, you can accomplish that by using AS path prepend on the routes you send from R2 to the ISP.

Regards,