Suppose I have a network like the one below.
All routers are running OSPF in the backbone. R5 is an ABR with customers connecting via PPPoE. I want all customers except Cust1 to reach the internet via R4,R3,R2,R1 EXCEPT Cust1 who I would like to route via R6,R1.
However, if any of the links from R5 to R1 fail I would like all traffic to go via R6
Can anyone help me with the best way to achieve this?