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300-410 Practice Question: An engineer enables unicast RPF (uRPF) in strict…
An engineer enables unicast RPF (uRPF) in strict mode on an interface. Afterward, some legitimate traffic from a BGP neighbor is dropped. The neighbor has two paths to the router, and traffic may arrive on a different interface than the return path. What is the most likely explanation?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Strict uRPF drops packets if the source IP is not reachable via the receiving interface, which fails in asymmetric routing scenarios.
Strict uRPF checks that the source IP of incoming packets matches the routing table entry for the interface it arrived on. If asymmetric routing occurs, packets from a valid neighbor may arrive on a different interface than the return path, causing them to be dropped.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Strict uRPF drops packets if the source IP is not reachable via the receiving interface, which fails in asymmetric routing scenarios.
Why this is correct
Strict mode requires the source IP to be in the routing table with the same interface as the incoming packet.
- ✗
The uRPF 'allow-default' option was not configured, so default routes are ignored.
Why it's wrong here
Allow-default affects default routes, but the issue is asymmetric routing, not default routes.
- ✗
The neighbor's BGP updates have a source IP that is not in the routing table.
Why it's wrong here
If the source IP is not in the routing table, it would be dropped, but the scenario describes asymmetric routing.
- ✗
Loose mode should be used instead, but strict mode was configured by mistake.
Why it's wrong here
Loose mode would allow asymmetric routing, but the question asks for the explanation of the drop.
Quick reference
Asymmetric Encryption Algorithm Comparison
| Algorithm | Key Exchange | Signatures | Equivalent Security Key | Notes |
|---|---|---|---|---|
| RSA-3072 | Yes | Yes | 128-bit | Widely deployed; slow for bulk data |
| ECDSA P-256 | No | Yes | 128-bit | Fast signatures; standard TLS certs |
| ECDH / ECDHE | Yes | No | 128-bit | Perfect forward secrecy in TLS 1.3 |
| DH / DHE | Yes | No | 128-bit (3072-bit key) | Replaced by ECDHE in modern TLS |
| Ed25519 | No | Yes | ~128-bit | SSH keys, modern PKI |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.