hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer configures uRPF loose mode on an…
An engineer configures uRPF loose mode on an interface that is part of an IPv6 network with multiple equal-cost paths to the same destination via different interfaces. The router receives traffic from a source that is reachable via one of the paths, but the traffic arrives on a different interface. The traffic is dropped. Which is the most likely explanation?
⚠ Common exam trap
Cisco often tests the distinction between uRPF strict and loose modes, but the trap here is that candidates forget link-local addresses are not in the global routing table, leading them to incorrectly attribute the drop to a mode mismatch or routing table issue.
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
✓
The source address is a link-local address (fe80::), which is not installed in the global routing table, causing uRPF loose mode to drop the packet.
In uRPF loose mode, the router checks that the source address of an incoming packet has a matching entry in the routing table, but it does not require that the packet arrives on the interface used to reach that source. However, link-local addresses (fe80::/10) are not installed in the global IPv6 routing table; they are only reachable on the local link. Therefore, when a packet with a link-local source address arrives, uRPF loose mode finds no matching route and drops the packet, regardless of the interface.
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 source address is a link-local address (fe80::), which is not installed in the global routing table, causing uRPF loose mode to drop the packet.
Why this is correct
Correct. Link-local addresses are not in the routing table, so uRPF loose mode drops them.
- ✗
The router has 'ipv6 uRPF strict' configured instead of loose, but the show command indicates loose.
Why it's wrong here
Incorrect. The configuration is loose mode.
- ✗
The equal-cost paths cause the routing table to have multiple entries, and uRPF loose mode requires a single best path.
Why it's wrong here
Incorrect. uRPF loose mode works with multiple paths; it just needs any entry.
- ✗
The interface has an IPv6 ACL that denies the traffic before uRPF is applied.
Why it's wrong here
Incorrect. ACLs are applied before uRPF, but the question implies uRPF is the cause.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
Key term
IPv6 Next Hop Resolution
IPv6 Next Hop Resolution is the process a router uses to determine the next router or destination device to which a packet should be forwarded, based on the destination IPv6 address and the routing table.
Key term
uRPF
Unicast Reverse Path Forwarding is a network security feature that verifies the source address of incoming packets to prevent IP spoofing attacks.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.