Summary:
1. Configure a static, default route on R1 pointing to the ISP.
2. Configure a static default route on R2 pointing to R1
3. Configure a static default route on R3 pointing to R2.
4. Option: using RIP for R2 and R3 rather than the static default routes.
1. Configure a static, default route on R1 pointing to the ISP.
R1.
ip route 0.0.0.0 0.0.0.0 192.168.1.100
#Test: add a couple of loopback IPs on ISP so we can test
int l0
ip address 4.2.2.2 255.255.255.255
int l1
ip address 8.8.8.8 255.255.255.255
2. Configure a static default route on R2 pointing to R1
R2.
ip route 0.0.0.0 0.0.0.0 10.24.0.1
#Test: you can't ping 4.2.2.2 at this point because ISP doesn't have a route back to R2 since ISP doesn't know anything about 10.24.0.0/24 network. However, you can test ping to R1's serial port because R1 does know how to get back to R2.
3. Configure a static default route on R3 pointing to R2.
R3.
ip route 0.0.0.0 0.0.0.0 10.15.1.13
#Test: ping to R1's serial/WAN port
4. Option: using RIP for R2 and R3 rather than the static default routes.
R2.
no ip route 0.0.0.0 0.0.0.0 10.24.0.1
R3.
no ip route 0.0.0.0 0.0.0.0 10.15.1.13
R1.
router rip
default-information originate
#Test:
-Yu