- A
It requires the source address to be reachable via the same interface.
Why wrong: That is strict mode.
- B
It only verifies that the source address exists in the FIB.
Loose mode checks for any route to the source address.
- C
It drops packets with link-local source addresses.
Why wrong: uRPF does not inherently drop link-local addresses; it checks routing table presence.
- D
It is enabled by default on all interfaces.
Why wrong: uRPF must be explicitly configured.
Question 1,556 of 2,152
300-410 IPv6 Traffic Filtering and uRPF Practice Question
This 300-410 practice question tests your understanding of ipv6 traffic filtering and urpf. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which statement about IPv6 uRPF loose mode is true?
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
✓
It only verifies that the source address exists in the FIB.
In IPv6 unicast Reverse Path Forwarding (uRPF) loose mode, the router checks the FIB (Forwarding Information Base) to verify that the source address of an incoming packet exists in the routing table. It does not require the source address to be reachable via the same interface, which is the key distinction from strict mode. This allows loose mode to be used in asymmetric routing scenarios where the return path may not match the ingress interface.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It requires the source address to be reachable via the same interface.
Why it's wrong here
That is strict mode.
- ✓
It only verifies that the source address exists in the FIB.
Why this is correct
Loose mode checks for any route to the source address.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
It drops packets with link-local source addresses.
Why it's wrong here
uRPF does not inherently drop link-local addresses; it checks routing table presence.
- ✗
It is enabled by default on all interfaces.
Why it's wrong here
uRPF must be explicitly configured.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse loose mode with strict mode, assuming loose mode still requires interface-level reachability, when in fact it only checks for the source address's existence in the FIB.
Detailed technical explanation
How to think about this question
Under the hood, uRPF loose mode performs a FIB lookup on the source address using the 'ipv6 verify unicast source reachable-via any' command. If the source address is not present in the FIB at all, the packet is dropped. This is useful in multihomed networks with asymmetric routing, where strict mode would incorrectly drop legitimate traffic. A real-world scenario is an ISP edge router receiving customer traffic from multiple upstream paths; loose mode allows the router to accept packets as long as the source is globally reachable, even if the ingress interface differs from the best return path.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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 |
What to study next
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FAQ
Questions learners often ask
What does this 300-410 question test?
IPv6 Traffic Filtering and uRPF — This question tests IPv6 Traffic Filtering and uRPF — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: It only verifies that the source address exists in the FIB. — In IPv6 unicast Reverse Path Forwarding (uRPF) loose mode, the router checks the FIB (Forwarding Information Base) to verify that the source address of an incoming packet exists in the routing table. It does not require the source address to be reachable via the same interface, which is the key distinction from strict mode. This allows loose mode to be used in asymmetric routing scenarios where the return path may not match the ingress interface.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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