Comprehensive and Detailed In-Depth Explanation:
Understanding the BGP Network Topology in the Question:
BGP Peering & Route Distribution
Each router forms EBGP peer relationships with directly connected neighbors.
R1 and R4 import the static route 192.168.1.0/24 into BGP and advertise it to their peers.
Community attributes are attached to routes to influence routing policies.
Effect of Community Attribute 1:1
R1 marks 192.168.1.0/24 with community 1:1 before advertising it.
R3 has a policy that rejects any routes with community attribute 1:1.
Since R1’s advertisement contains 1:1, R3 will not accept 192.168.1.0/24 from R2.
Route Selection and Traffic Flow Analysis:
R1 advertises 192.168.1.0/24 with community 1:1 to R2.
R3 rejects this route from R2 because of the configured routing policy.
R4 also advertises 192.168.1.0/24 to its EBGP neighbors without community 1:1.
R5 learns the route from R4 and advertises it to R3.
Since R5’s advertisement does not include community 1:1, R3 accepts the route from R5.
Thus, the best available path for R3 to reach 192.168.1.0/24 is R3 → R5 → R1.
✅ Correct Path: R3 → R5 → R1
Checking Each Option:
❌ Option A: R3 → R2 → R4 (Incorrect)
R3 does not learn the route from R2 because it rejects community 1:1.
Since R1 added 1:1, and R2 propagated the same community, R3 will not accept this path.
❌ Option B: R3 does not have a route to 192.168.1.0/24 (Incorrect)
R3 does have a route, but it learns it from R5 instead of R2.
❌ Option C: R3 → R2 → R1 (Incorrect)
R1 marked the route with 1:1, and R2 advertised it with the same community.
Since R3 rejects 1:1 routes, it will not use this path.
✅ Option D: R3 → R5 → R1 (Correct)
R5 learns the route from R4, which does not have community 1:1, and advertises it to R3.
R3 accepts this route and forwards traffic to R5, which sends it to R1.
Final Conclusion:
✅ D. The correct path for traffic from R3 to 192.168.1.0/24 is R3 → R5 → R1.
Thus, the correct answer is: D.
[Reference:, HCIP-Datacom-Advanced Routing & Switching Technology V1.0 – BGP Route Filtering and Community Attribute Configuration, Huawei Official HCIP-Datacom Study Guide – BGP Best Path Selection and Community-Based Routing Policies, Huawei Documentation on BGP Community Attributes and Route Filtering, , , , ]
