Section 1 Task 4.12 OSPF Domain-ID
Hi all !! this is my first post in the community.
I was working on this task and I noticed 2 weird things about the explanations provided :
- After completing all redistribution, R1 should see two paths to reach 220.127.116.11/32, one via backdoor link (XR2) and one via MPLS L3VPN, and the provided output compares the generated LSA's. But with my understanding in this situation, R1, being an ABR, should never be able to calculate an inter-area path through a non-backbone area, even if it knows about the related summary LSA's. If you disable the MPLS VPN part (the backdoor link being the only option) , you should not see the inter-area route appear on the routing table (at least that's what happened in my case). So for me the reason why R1 prefers the MPLS VPN link is not related to the cost but to the global design mixing non-backbone areas.
- According to solution, the external route (10.20.20.20/32) is prefered via the backdoor link (on R1) because the PE (R2) would not reoriginate a type-5 LSA if someone else in the area is already originating it, but is this point correct even if the router-ids are different?? (forwarding addressess being both set to 0.0.0.0). For me , what is happening is simply that R2 , when redistributing ospf external route in BGP, will have 2 MBGP routes for the same prefix 10.20.20.20/32: one coming from redistribution, so the weight is set to 32768 (default behaviour) , and one coming from MPLS VPN (weight to 0). The weight attribute would play and R2 would prefer the path via R1, so no reason to generate a type-5 LSA. --> Maybe that was the initial idea of the provided explanation, but I didn't get it that way..