hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer configures unicast Reverse Path…
An engineer configures unicast Reverse Path Forwarding (uRPF) in strict mode on an interface. After configuration, legitimate traffic from a directly connected network is being dropped. Which 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
✓
Asymmetric routing is causing the return path to use a different interface.
Strict uRPF checks that the source IP address of incoming packets has a route in the routing table that points back to the same interface. If there is asymmetric routing where the return path uses a different interface, strict uRPF will drop the traffic. This is a common edge case in networks with multiple paths.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Asymmetric routing is causing the return path to use a different interface.
Why this is correct
Strict uRPF requires the source IP to be reachable via the same interface it arrived on. Asymmetric routing violates this, causing drops.
- ✗
The 'allow-default' option is not configured, and a default route exists.
Why it's wrong here
The 'allow-default' option is for loose mode, not strict mode.
- ✗
The interface is configured with an IP address that is not in the routing table.
Why it's wrong here
This would cause other issues, but uRPF checks the source IP, not the interface IP.
- ✗
The routing table has a more specific route for the source network via a different interface.
Why it's wrong here
This is exactly the condition that causes strict uRPF to drop, but it is due to asymmetric routing, not just a more specific route.
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
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