Hi all,
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?

Many thanks,

NTB

There was a presentation at MuM USA 2017 which gives a way to do this using eBGP

https://www.youtube.com/watch?v=dFZz2z6RdQY

Thanks for the reply,
R1 is already announcing our /22 on BGP. At the moment we just get a default route from our upstream although this may change in the next few months. Meanwhile I'll look at the video

NTB
8o

You can't do this with OSPF, hence, Open Shortest Path First in the name. All traffic will traverse R6, unless the path becomes unavailable. If Cust2 to Cust4 somehow is tunneled to R3, possibilities opens up with OSPF and then it could become interesting though.

At best, you're looking at VPLS Tunnels / Traffic Engineering, VRFs, or static policy routes (perhaps even a combination of those). Even with BGP between R1-R6, the configuration will be very, very, complex IMHO.

You can't do this with OSPF, hence, Open Shortest Path First in the name. All traffic will traverse R6, unless the path becomes unavailable. If Cust2 to Cust4 somehow is tunneled to R3, possibilities opens up with OSPF and then it could become interesting though.

At best, you're looking at VPLS Tunnels / Traffic Engineering, VRFs, or static policy routes (perhaps even a combination of those). Even with BGP between R1-R6, the configuration will be very, very, complex IMHO.

Complexity is all relative. The first question to ask is "How complex is this as compared to the alternative solution?" Typically,if you have a business requirement that results in added complexity, it's important to verify the added complexity is stable and scalable.

Simple networks that meet your requirements are awesome
Simple networks that don't solve the problems you have are useless