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300-410 Practice Question: An engineer enables uRPF (unicast Reverse Path…
An engineer enables uRPF (unicast Reverse Path Forwarding) in strict mode on an interface connected to a DMVPN spoke. The spoke has multiple tunnels and receives traffic from the hub with a source IP that is not the best reverse path. Unexpectedly, the spoke drops all traffic from the hub, even though the hub is reachable via the tunnel. 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
✓
uRPF strict mode requires the reverse path to be via the same interface; asymmetric routing causes drops.
uRPF strict mode checks that the source IP of incoming packets has a route back to the source via the same interface. In DMVPN, the hub's source IP may be reachable via a different interface (e.g., physical interface) than the tunnel interface where the packet arrives. This asymmetric routing causes uRPF strict mode to drop the packets. The solution is to use loose mode or allow-default.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
uRPF strict mode requires the reverse path to be via the same interface; asymmetric routing causes drops.
Why this is correct
Strict mode fails if the return route uses a different interface, which is common in DMVPN.
- ✗
The hub's IP address is not in the routing table, so uRPF drops the packet.
Why it's wrong here
The hub is reachable, but via a different path.
- ✗
uRPF must be configured with the `allow-default` option to accept packets with default route.
Why it's wrong here
Allow-default helps if the default route is used, but the issue is asymmetric routing.
- ✗
uRPF is not supported on tunnel interfaces; it must be applied on the physical interface.
Why it's wrong here
uRPF is supported on tunnel interfaces.
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.