easyMultiple Choice
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 is selected only with the 'any' keyword; omitting it defaults to strict mode, which requires the source be reachable via the receiving interface. It tempts because loose mode is the common alternative, but strict is the documented default for this command.
- ✓
Strict mode (rx)
Why this is correct
Configuring ipv6 verify unicast source reachable-via without a keyword enables strict mode, equivalent to the rx keyword. The router checks that the source is reachable via the same interface the packet arrived on, dropping packets that fail this reverse-path check.
- ✗
No uRPF is applied
Why it's wrong here
Configuring the command enables uRPF; it does not leave verification disabled. It tempts because uRPF is absent until explicitly configured, but once the interface command is entered, strict mode applies by default, dropping packets failing the reverse-path check.
- ✗
Only default routes are allowed
Why it's wrong here
uRPF checks the source address against the routing table, not merely default routes; no such default-route-only behaviour exists for this command. It tempts as a shortcut for edge filtering, but the actual default is strict mode.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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