Lab8 MPLS + Shadow RR

Load unix:lab8.init.cfg

configure replace unix:lab8.init.cfg

R8 has been added as an additional RR, and all iBGP sessions have been preconfigured. R5 is setting LP to 50 on the routes received from R6.

Without using Add Path capability negotiation, configure R8 as a shadow RR to reflect the backup path to R2. On R2, install this as a backup path.

Note that this will not work for 6PE, but you can configure it anyways.

Answer

https://www.youtube.com/watch?v=GlBXdYHvWmg&list=PL3Y9eZjZCcsejbVWD3wJIePqe3NiImqxB&index=11

#R5
router bgp 65000
 add ipv4
  bgp advertise-best-external
 add ipv6
  bgp advertise-best-external

#R8
router bgp 65000
 add ipv4
  bgp additional-paths select backup
  neighbor 10.0.0.2 advertise diverse-path backup
 add ipv6
  bgp additional-paths select backup
  neighbor 10.0.0.2 advertise diverse-path backup

#R2
router bgp 65000
 add ipv4
  bgp additional-paths select backup
  bgp additional-paths install
 add ipv6
  bgp additional-paths select backup
  bgp additional-paths install

Explanation/Verification

R5 is hiding its external path again, because the LP is lower than the path via R4. To get around this without using the Add Path feature, we use advertise-best-external.

#R5
router bgp 65000
 add ipv4
  bgp advertise-best-external
 add ipv6
  bgp advertise-best-external

R8 will now receive the path via R5. However, there is a bug with 6PE. R5 is not including a service label, so R8 is marking this as inaccessible. We can ignore IPv6 for the rest of the lab.

R8 now needs to mark the backup path and advertise this as the only path to R2. Because we are not using the Add Path feature, we can use the advertise diverse-path feature.

#R8
router bgp 65000
 add ipv4
  bgp additional-paths select backup
  neighbor 10.0.0.2 advertise diverse-path backup
 add ipv6
  bgp additional-paths select backup
  neighbor 10.0.0.2 advertise diverse-path backup

On R2, we will now have both paths. We simply need to identify the backup path and install it as a repair route.

#R2
router bgp 65000
 add ipv4
  bgp additional-paths select backup
  bgp additional-paths install
 add ipv6
  bgp additional-paths select backup
  bgp additional-paths install

Remember that R2, as the ingress PE, controls which egress PE is used. When it loses the path via R4, it will immediately switchover to R5. R3, as a P router in the core, simply switches on the top transport label and has no idea about the BGP routes.