正解：

Explanation:
* A = 50
* B = 10
* C = 20
Comprehensive and Detailed In-Depth Explanation:
Understanding OSPF Path Selection and Cost Calculation:
* OSPF selects the shortest path (lowest cost) to the destination.
* The OSPF cost is determined by the cumulative sum of interface costs along a path .
* By assigning specific costs to A, B, and C , we can influence OSPF's path selection to meet the desired routing behavior.
Step-by-Step Analysis of Required Traffic Flow:
1. Traffic from PC1 to PC2 must take the route:
PC1 - > R1 - > R3 - > R2 - > PC2
* To force traffic through R3 , the cost of the direct link R1 - > R2 (Cost-A) must be higher than the alternative path via R3 .
* We assign Cost-A = 50 (high cost) to discourage direct routing from R1 - > R2 .
* The cost of R1 - > R3 (Cost-C) should be lower , so we assign Cost-C = 20 .
* The cost of R3 - > R2 (default Cost-20) remains unchanged.
* Total cost via R3: 20 (R1- > R3) + 20 (R3- > R2) = 40 , which is less than the direct link of 50 , so OSPF prefers this path.
# Traffic follows: PC1 - > R1 - > R3 - > R2 - > PC2
2. Traffic from PC2 to PC1 must take the route:
PC2 - > R2 - > R1 - > PC1
* We need to make R2 - > R1 (Cost-B) the best (lowest cost) route for return traffic .
* Assign Cost-B = 10 (low cost).
* This ensures that R2 prefers the direct path R2 - > R1 instead of R2 - > R3 - > R1 (which costs
20+20=40).
# Traffic follows: PC2 - > R2 - > R1 - > PC1
Final Cost Assignments for Correct Routing Behavior:
Cost
Assigned Value
Reason
Cost-A (R1 - > R2)
50
High to discourage direct R1- > R2 routing
Cost-B (R2 - > R1)
10
Low to ensure PC2- > PC1 prefers direct R2- > R1
Cost-C (R1 - > R3)
20
Medium to encourage R1- > R3- > R2 path
Key Takeaways:
* Higher OSPF cost discourages path selection.
* Lower OSPF cost encourages path selection.
* By manipulating OSPF cost values, we achieve asymmetric routing between PC1 and PC2.
* This aligns with OSPF path selection principles covered in HCIP-Datacom certification.
HCIP-Datacom-Advanced Routing & Switching Technology References:
* Huawei HCIP-Datacom Official Certification Guide , Chapter on OSPF Cost Calculation and Path Selection .
* Huawei Enterprise Networking Training Materials , OSPF Path Optimization Techniques.
* Huawei Datacom Configuration Guide , OSPF Cost and Traffic Engineering.