The correct answer is that the router performs loose uRPF, meaning the source address must be reachable via any route in the FIB. This is because the command `ipv6 verify unicast source reachable-via any` explicitly enables loose mode verification, which checks only that a valid route to the source exists somewhere in the routing table—without requiring that the incoming interface matches the reverse path interface. On the Cisco CCNP ENARSI 300-410 exam, this configuration tests your understanding of uRPF modes and their anti-spoofing behavior; a common trap is confusing loose mode with strict mode, which demands both route existence and interface match. Remember the memory tip: “Loose is lenient—any route will do; strict is specific—same interface, too.”
300-410 IPv6 Traffic Filtering and uRPF Practice Question
This 300-410 practice question tests your understanding of ipv6 traffic filtering and urpf. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Examine this configuration:
interface GigabitEthernet0/4
ipv6 address 2001:db8:2::1/64
ipv6 verify unicast source reachable-via any
What is the effect of the 'ipv6 verify unicast source reachable-via any' command?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The router performs loose uRPF: the source address must be reachable via any route in the FIB.
This enables uRPF (unicast Reverse Path Forwarding) in loose mode. It checks that the source address of incoming packets is reachable via any route in the FIB, but does not require the exact interface.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 router performs strict uRPF: the source address must be reachable via the same interface the packet arrived on.
Why it's wrong here
The 'any' keyword indicates loose mode, not strict.
✓
The router performs loose uRPF: the source address must be reachable via any route in the FIB.
Why this is correct
Loose mode only requires a route to the source, not necessarily via the receiving interface.
The router drops all packets with source addresses not in the same subnet as the interface.
Why it's wrong here
Loose mode does not require the source to be in the same subnet; it only checks for a route.
✗
The command is invalid because 'ipv6 verify unicast' requires a route-map.
Why it's wrong here
The command is valid; the 'reachable-via any' option is a standard uRPF configuration.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Trap categories for this question
Keyword trap
The 'any' keyword indicates loose mode, not strict.
Command / output trap
The command is valid; the 'reachable-via any' option is a standard uRPF configuration.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 300-410 subnetting questions on CIDR, address ranges, and subnet selection.
IPv6 Traffic Filtering and uRPF — This question tests IPv6 Traffic Filtering and uRPF — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The router performs loose uRPF: the source address must be reachable via any route in the FIB. — This enables uRPF (unicast Reverse Path Forwarding) in loose mode. It checks that the source address of incoming packets is reachable via any route in the FIB, but does not require the exact interface.
What should I do if I get this 300-410 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 300-410 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
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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 statement about IPv6 uRPF loose mode is true?
medium
A.It requires the source address to be reachable via the same interface.
✓ B.It only verifies that the source address exists in the FIB.
C.It drops packets with link-local source addresses.
D.It is enabled by default on all interfaces.
Why B: Loose mode only checks that the source address is present in the routing table, regardless of the incoming interface.
Last reviewed: Jun 18, 2026
Question Discussion
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