- A
Strict mode uRPF drops packets if the source address is not reachable via the incoming interface.
Correct. Strict mode requires the source prefix to be reachable via the exact incoming interface.
- B
Loose mode uRPF drops packets if the source address is not present in the FIB at all.
Correct. Loose mode only checks that the source address exists in the FIB, ignoring the interface.
- C
The default uRPF mode on Cisco IOS-XE is strict mode.
Why wrong: Incorrect. The default is loose mode when 'ipv6 verify unicast source reachable-via' is configured without specifying 'rx'.
- D
IPv6 uRPF can be applied globally using the 'ipv6 unicast-rpf' command.
Why wrong: Incorrect. IPv6 uRPF is configured per interface using 'ipv6 verify unicast source reachable-via', not globally.
- E
uRPF checks both source and destination addresses in the IPv6 header.
Why wrong: Incorrect. uRPF only verifies the source address against the FIB; destination address is not checked.
Quick Answer
The correct answer is that loose mode uRPF drops packets if the source address is not present in the FIB at all, while strict mode additionally requires the source prefix to match the incoming interface. This distinction is critical because IPv6 uRPF verifies the source address against the Forwarding Information Base (FIB), not the destination. Strict mode, enabled with `ipv6 verify unicast source reachable-via rx`, demands both a FIB match and that the return path exits the same interface, making it vulnerable to dropping legitimate traffic under asymmetric routing. Loose mode, set with `reachable-via any`, only checks for any FIB entry for the source, ignoring the interface, which is more tolerant of asymmetric paths but still blocks packets with completely bogus source addresses. On the Cisco CCNP ENARSI 300-410 exam, this topic tests your ability to differentiate between the two modes and their configuration commands, often with a trap involving the default mode—remember, the default is loose, not strict. A simple memory tip: “Strict is strict on the interface; Loose is loose on the interface.”
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 TWO statements about IPv6 unicast RPF (uRPF) behavior in Cisco IOS-XE are correct? (Choose TWO.)
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 mode uRPF drops packets if the source address is not reachable via the incoming interface.
IPv6 uRPF verifies the source address of incoming packets against the FIB. Strict mode requires the source address to match the FIB entry for the incoming interface and the exact prefix. Loose mode only requires a matching FIB entry, ignoring the interface. The default is loose mode. The 'ipv6 verify unicast source reachable-via any' command enables loose mode, while 'ipv6 verify unicast source reachable-via rx' enables strict mode. uRPF is applied per interface and does not check the destination address. It can drop packets with legitimate source addresses if asymmetric routing is present.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 mode uRPF drops packets if the source address is not reachable via the incoming interface.
Why this is correct
Correct. Strict mode requires the source prefix to be reachable via the exact incoming interface.
Related concept
Static NAT maps one inside address to one outside address.
- ✓
Loose mode uRPF drops packets if the source address is not present in the FIB at all.
Why this is correct
Correct. Loose mode only checks that the source address exists in the FIB, ignoring the interface.
Related concept
Static NAT maps one inside address to one outside address.
- ✗
The default uRPF mode on Cisco IOS-XE is strict mode.
Why it's wrong here
Incorrect. The default is loose mode when 'ipv6 verify unicast source reachable-via' is configured without specifying 'rx'.
- ✗
IPv6 uRPF can be applied globally using the 'ipv6 unicast-rpf' command.
Why it's wrong here
Incorrect. IPv6 uRPF is configured per interface using 'ipv6 verify unicast source reachable-via', not globally.
- ✗
uRPF checks both source and destination addresses in the IPv6 header.
Why it's wrong here
Incorrect. uRPF only verifies the source address against the FIB; destination address is not checked.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
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IPv6 Traffic Filtering and uRPF — study guide chapter
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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 — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Strict mode uRPF drops packets if the source address is not reachable via the incoming interface. — IPv6 uRPF verifies the source address of incoming packets against the FIB. Strict mode requires the source address to match the FIB entry for the incoming interface and the exact prefix. Loose mode only requires a matching FIB entry, ignoring the interface. The default is loose mode. The 'ipv6 verify unicast source reachable-via any' command enables loose mode, while 'ipv6 verify unicast source reachable-via rx' enables strict mode. uRPF is applied per interface and does not check the destination address. It can drop packets with legitimate source addresses if asymmetric routing is present.
What should I do if I get this 300-410 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on 300-410
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which THREE statements about IPv6 unicast RPF (uRPF) are true? (Choose THREE.)
hard- ✓ A.IPv6 uRPF uses the Forwarding Information Base (FIB) to verify source address reachability.
- ✓ B.IPv6 uRPF can be configured in strict mode or loose mode.
- ✓ C.IPv6 uRPF is configured on a per-interface basis.
- D.IPv6 uRPF checks the destination address of incoming packets.
- E.IPv6 uRPF is used to filter multicast traffic.
Why A: uRPF uses the FIB (CEF) for lookups, it can operate in strict or loose mode, and it is applied per interface. The other options are false: uRPF does not inspect the destination address (only source), and it is not used for multicast traffic.
Last reviewed: Jun 18, 2026
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