Cisco
352-001 · Question #27
352-001 Question #27: Real Exam Question with Answer & Explanation
The correct answer is A: create a tunnel between R2 and R3. A tunnel between R2 and R3 resolves the IBGP next-hop reachability problem that prevents traffic from Network A from reaching Network B across the two BGP border routers.
Question
Refer to the exhibit. R2 and R3 are running EBGP and are learning Network A and Network B. R2 and R3 are also running IBGP to exchange Network A and Network B. OSPF is IGP. R2 and R3 are advertising default routes. R1 and R4 can send and receive traffic from Network A and Network B respectively. However, Network A cannot send traffic to Network B. How can you solve this problem?
Exhibit
Options
- Acreate a tunnel between R2 and R3
- Bcreate a tunnel between R2 and R4
- Ccreate static default routes pointing from R1 and R4 to R2 and R3, respectively
- Dconvert R3 and R2 to ABRs so that R1 and R4 can choose the closest ABR to exit the network
Explanation
A tunnel between R2 and R3 resolves the IBGP next-hop reachability problem that prevents traffic from Network A from reaching Network B across the two BGP border routers.
Common mistakes.
- B. A tunnel between R2 and R4 bypasses R3 entirely and does not address the IBGP next-hop reachability issue between R2 and R3 that blocks Network A-to-Network B traffic.
- C. Static default routes from R1 and R4 pointing to R2 and R3 only affect how R1 and R4 reach their local exit points and do not resolve the forwarding failure between R2 and R3.
- D. Converting R2 and R3 to OSPF ABRs is an IGP concept unrelated to BGP next-hop reachability and would not fix the inter-domain forwarding path between the two EBGP border routers.
Concept tested. IBGP next-hop reachability and GRE tunnel as solution
Reference. https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html
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