The correct answer is deny ipv6 any 2001:db8:1::/48. This entry is correct because in an IPv6 ACL, the deny keyword is followed by the protocol (ipv6), then the source, and then the destination prefix; the any keyword matches all source addresses, and the destination prefix 2001:db8:1::/48 is specified directly after it, exactly as required to block traffic to that entire subnet. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding of IPv6 ACL syntax and the order of operands, which is a common pitfall—many candidates mistakenly place the destination before the source or forget the protocol keyword. A frequent trap is confusing the IPv4 ACL structure, where the source comes first, with the identical IPv6 order, but the key is to remember that both IPv4 and IPv6 ACLs follow the same sequence: action, protocol, source, destination. For a memory tip, think “Deny any to the prefix” as the natural flow: deny ipv6 any [prefix].
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 IPv6 access-list entry will deny traffic from any source to the destination prefix 2001:db8:1::/48?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
deny ipv6 any 2001:db8:1::/48
The 'any' keyword matches any source, and the destination prefix is specified after the deny keyword.
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.
✓
deny ipv6 any 2001:db8:1::/48
Why this is correct
This correctly denies all IPv6 traffic from any source to the specified destination prefix.
Related concept
Static NAT maps one inside address to one outside address.
✗
deny ipv6 2001:db8:1::/48 any
Why it's wrong here
This denies traffic from the specified source to any destination, which is the opposite of what is asked.
✗
deny ipv6 any host 2001:db8:1::1
Why it's wrong here
This denies traffic to a single host, not the /48 prefix.
✗
deny ipv6 2001:db8:1::/48 2001:db8:1::/48
Why it's wrong here
This denies traffic from the prefix to itself, which is not the intended behavior.
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.
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: deny ipv6 any 2001:db8:1::/48 — The 'any' keyword matches any source, and the destination prefix is specified after the deny keyword.
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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Question Discussion
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