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300-410 Practice Question: The default uRPF mode when 'ipv6 verify unicast…
What is the default uRPF mode when 'ipv6 verify unicast source reachable-via' is configured without any keyword?
⚠ Common exam trap
Cisco often tests the default behavior of commands without keywords, and the trap here is that candidates mistakenly assume 'ipv6 verify unicast source reachable-via' defaults to loose mode or requires an explicit keyword to enable uRPF, when in fact strict mode is the default.
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
✓
Strict mode (rx)
When 'ipv6 verify unicast source reachable-via' is configured without any keyword, the default mode is strict (rx). In strict mode, the router checks that the source address of an incoming IPv6 packet is reachable via the exact interface on which the packet was received, using the FIB. This prevents source address spoofing by ensuring the return path matches the ingress 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.
- ✗
Loose mode (any)
Why it's wrong here
Loose mode requires the 'any' keyword; the default is strict.
- ✓
Strict mode (rx)
Why this is correct
Without keywords, the router uses strict uRPF, checking the source is reachable via the receiving interface.
- ✗
No uRPF is applied
Why it's wrong here
The command itself enables uRPF; the default mode is strict.
- ✗
Only default routes are allowed
Why it's wrong here
That would be 'allow-default', which is not the default.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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