- A
When both uRPF and an inbound IPv6 ACL are configured on the same interface, uRPF is processed first.
Correct. uRPF checks occur before ACL processing in the input path.
- B
An IPv6 ACL can be used to permit traffic that would otherwise be dropped by uRPF strict mode due to asymmetric routing.
Correct. You can use an ACL to explicitly permit traffic from sources that are not reachable via the incoming interface, bypassing uRPF drops.
- C
uRPF can be configured to ignore IPv6 ACLs on the same interface.
Why wrong: Incorrect. uRPF and ACLs are independent; uRPF does not ignore ACLs. They operate sequentially.
- D
An outbound IPv6 ACL can be used to filter traffic before uRPF checks.
Why wrong: Incorrect. uRPF checks occur on inbound traffic only; outbound ACLs are processed after routing, not before uRPF.
- E
If uRPF drops a packet, the inbound ACL is still evaluated for logging purposes.
Why wrong: Incorrect. If uRPF drops a packet, it is discarded before reaching the ACL, so the ACL is not evaluated.
Quick Answer
The answer is that an IPv6 ACL can be used to permit traffic that would otherwise be dropped by uRPF strict mode due to asymmetric routing. This is correct because on a Cisco router, uRPF processes packets before inbound ACLs in the input path; if uRPF drops a packet, the ACL is never evaluated, but if uRPF passes the packet, the ACL then filters it sequentially. For the CCNP ENARSI 300-410 exam, this interaction tests your understanding of packet flow order and the fact that ACLs can override uRPF drops only when explicitly configured to permit the traffic, which is a common trap—many candidates mistakenly think uRPF always overrides ACLs. Remember the memory tip: “uRPF first, ACL second; to save a packet from uRPF, the ACL must be beckoned.”
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 the interaction between IPv6 ACLs and uRPF 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
When both uRPF and an inbound IPv6 ACL are configured on the same interface, uRPF is processed first.
IPv6 ACLs and uRPF can be applied together on the same interface. uRPF processes packets before inbound ACLs in the input path. If uRPF drops a packet, the ACL is not evaluated. Conversely, if uRPF passes the packet, the ACL then filters it. ACLs can be used to permit traffic that uRPF would otherwise drop (e.g., for asymmetric routing), but that requires careful design. uRPF does not override ACLs; they work sequentially.
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.
- ✓
When both uRPF and an inbound IPv6 ACL are configured on the same interface, uRPF is processed first.
- ✓
An IPv6 ACL can be used to permit traffic that would otherwise be dropped by uRPF strict mode due to asymmetric routing.
- ✗
uRPF can be configured to ignore IPv6 ACLs on the same interface.
Why it's wrong here
Incorrect. uRPF and ACLs are independent; uRPF does not ignore ACLs. They operate sequentially.
- ✗
An outbound IPv6 ACL can be used to filter traffic before uRPF checks.
Why it's wrong here
Incorrect. uRPF checks occur on inbound traffic only; outbound ACLs are processed after routing, not before uRPF.
- ✗
If uRPF drops a packet, the inbound ACL is still evaluated for logging purposes.
Why it's wrong here
Incorrect. If uRPF drops a packet, it is discarded before reaching the ACL, so the ACL is not evaluated.
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: When both uRPF and an inbound IPv6 ACL are configured on the same interface, uRPF is processed first. — IPv6 ACLs and uRPF can be applied together on the same interface. uRPF processes packets before inbound ACLs in the input path. If uRPF drops a packet, the ACL is not evaluated. Conversely, if uRPF passes the packet, the ACL then filters it. ACLs can be used to permit traffic that uRPF would otherwise drop (e.g., for asymmetric routing), but that requires careful design. uRPF does not override ACLs; they work sequentially.
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. Consider the following configuration: ipv6 access-list FILTER permit ipv6 2001:db8:3::/48 any deny ipv6 any any interface GigabitEthernet0/5 ipv6 traffic-filter FILTER in ipv6 verify unicast source reachable-via rx A packet arrives on GigabitEthernet0/5 with source 2001:db8:3::100 and destination 2001:db8:4::1. The route for 2001:db8:3::/48 points out interface GigabitEthernet0/6. What happens?
medium- A.The packet is permitted because the ACL matches and uRPF is not applied.
- ✓ B.The packet is dropped by uRPF because strict mode requires the source to be reachable via the receiving interface.
- C.The packet is dropped by the ACL because the deny statement blocks all traffic.
- D.The packet is permitted because uRPF only checks destination addresses.
Why B: The ACL permits the packet (source matches prefix). However, uRPF in strict mode (rx) checks that the source is reachable via the same interface the packet arrived on. Since the route points to a different interface, uRPF drops the packet.
Last reviewed: Jun 18, 2026
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