CCNA LEVEL CHALLENGE:

You have the following topology, as you can see I only have 2 routers, so it is not a CCIE level, this challenge is CCNA level, because what can you do with two routers, right?
These two routers are connected via their serial interfaces. You can use any serial interface that you want.
R1- 12.1.1.1/30 (S1/2) --------------------- (S1/1) 12.1.1.2/30
• Configure PPP encapsulation between R1 and R2 serial connection.
• R2 should negotiate the 12.1.1.2 address from R1.
• R2's subnet mask must be /30. * DO NOT USE DHCP ON R1 to accomplish this task.
• R2 must install a default route through R1. * DO NOT USE ANY STATIC OR DYNAMIC ROUTING PROTOCOL FOR INSTALLING THIS DEFAULT ROUTE ON R2 *
• R1 is not allowed to install a /32 route for R2's negotiated address.
• R1 and R2 must authenticate each other using CHAP using the following parameters:
Username: PPPUser
Password: CISCO

This means that they should both use the same Username and password.