Lab5 Shadow RR

Load unix:lab5.init.cfg

configure replace unix:lab5.init.cfg

R8 has been introduced as a second RR.

• Configure this as a shadow RR so that R8 advertises the backup path via R5 to all route-reflector clients.

  • The second RR session has already been configured on all routers within 65000.

• R3 is already configured for iBGP multipath.

• Ensure that the RRs make the same bestpath decision, no matter where they are placed in the IGP topology.

Answer

https://www.youtube.com/watch?v=LB08hAqTQVQ&list=PL3Y9eZjZCcsejbVWD3wJIePqe3NiImqxB&index=7

#R7
router bgp 65000
 add ipv4
  bgp bestpath igp-metric ignore
 add ipv6
  bgp bestpath igp-metric ignore

#R8
router bgp 65000
 !
 add ipv4
  bgp bestpath igp-metric ignore
  bgp additional-paths select backup
 add ipv6
  bgp bestpath igp-metric ignore
  bgp additional-paths select backup
 !
 template peer-policy IBGP_V4V6
  advertise diverse-path backup
 exit-peer-policy

Explanation

To guarantee that the two RRs (R7 and R8) will choose the same primary bestpath no matter where they are in the topology, we must disable the IGP metric comparison in the bestpath decision process. This ensures that the RRs always select the same bestpath.

#R7, R8
router bgp 65000
 add ipv4
  bgp bestpath igp-metric ignore
 add ipv6
  bgp bestpath igp-metric ignore

Next, on R8, we must only advertise the diverse backup path to all RR clients. We select the backup path, and then advertise this to peers using the template peer-policy. Note that the backup paths must be first selected before you can apply the advertisement of the backup path in the template. You may need to clear ip bgp * after applying the config.

#R8
router bgp 65000
 !
 add ipv4
  bgp additional-paths select backup
 add ipv6
  bgp additional-paths select backup
 !
 template peer-policy IBGP_V4V6
  advertise diverse-path backup
 exit-peer-policy

Verification

On R8, we can see that it is advertising the backup path to all RR clients.

R3 selects this for multipath consideration and installs both paths for load sharing. (The multipath configuration was already preconfigured in this lab).