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.