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.
A network engineer runs the following command to debug IPv6 traffic filtering:
R1# debug ipv6 packet access-list FILTER detail
IPv6 packet debugging is on for access list FILTER (detail)
*Mar 1 00:01:23.456: IPv6: source 2001:DB8:2::1 (GigabitEthernet0/0)
*Mar 1 00:01:23.456: dest 2001:DB8:3::1 (GigabitEthernet0/1)
*Mar 1 00:01:23.456: traffic class 0, flowlabel 0, hlim 64, next header 6 (TCP)
*Mar 1 00:01:23.456: denied by access-list FILTER
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The packet is denied because the source address 2001:DB8:2::1 matches the deny entry in the access list.
The debug output shows an IPv6 packet from 2001:DB8:2::1 to 2001:DB8:3::1 being denied by access-list FILTER. This matches the deny statement for the 2001:DB8:2::/48 prefix.
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.
✓
The packet is denied because the source address 2001:DB8:2::1 matches the deny entry in the access list.
Why this is correct
Correct. The debug clearly states the packet is denied by the access list, which has a deny for that source prefix.
Related concept
Static NAT maps one inside address to one outside address.
✗
The packet is permitted because it is a TCP packet.
Why it's wrong here
Incorrect. The debug shows it is denied regardless of protocol.
✗
The packet is denied because of uRPF check failure.
Why it's wrong here
Incorrect. The debug explicitly says 'denied by access-list FILTER', not uRPF.
✗
The packet is permitted because the destination is not in the access list.
Why it's wrong here
Incorrect. The access list filters based on source; the packet is denied.
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.
Trap categories for this question
Command / output trap
Incorrect. The debug shows it is denied regardless of protocol.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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.
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: The packet is denied because the source address 2001:DB8:2::1 matches the deny entry in the access list. — The debug output shows an IPv6 packet from 2001:DB8:2::1 to 2001:DB8:3::1 being denied by access-list FILTER. This matches the deny statement for the 2001:DB8:2::/48 prefix.
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.
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