1. R1 will route all packets destined to area 1 to R2, since that is the ABR that advertises reachability to area 1 destinations to area 2. By creating the virtual link, R2 also becomes a backbone router. So there will not be any sub-optimal routing as such.
2. If all interfaces on R2 are disabled, there is really no way for R1 to get through R2, is there ? So area 2 will get completely partitioned from area 2 and area 0.
3. If all interfaces on R3 are disabled, the virtual link will go down. The behaviour here is really implementation-dependent. The Cisco ABR behaviour follows RFC3509 - 'Alternative Implementations of OSPF Area Border Routers'. As per this RFC, R2 in your example will not be considered an ABR and will not generate inter-area summaries into the 2 areas. Therefore, R1 will not be able to reach destinations in Area 1.
Another thing I should add: in an implementation compliant with RFC2328, the answer to your question 3 would be that R1 would be able to reach destinations in area 1, even if it had no connectivity to area 0.
Hi everyone, I would like to thank you in advance for any help you can provide a newcomer like myself!
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