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300-410 Practice Question: Interface GigabitEthernet0/1 is configured as…
Interface GigabitEthernet0/1 is configured as shown: interface GigabitEthernet0/1
ipv6 address 2001:db8:1::1/64 ipv6 nd raguard ipv6 nd prefix default no-autoconfig
What is the effect of this configuration?
⚠ Common exam trap
Cisco often tests the distinction between commands that affect outgoing RAs (like `ipv6 nd prefix default no-autoconfig`) versus those that filter incoming RAs (like `ipv6 nd raguard`), leading candidates to confuse the direction of the traffic being controlled.
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 interface drops all incoming Router Advertisements from other routers.
The `ipv6 nd raguard` command enables Router Advertisement (RA) guard on the interface, which drops all incoming RAs from other routers to prevent rogue RA attacks. The `ipv6 nd prefix default no-autoconfig` command suppresses the autonomous flag in sent RAs, but the RA guard is the active security feature that blocks incoming RAs, making option A correct.
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 interface drops all incoming Router Advertisements from other routers.
Why this is correct
IPv6 RA guard on the interface inspects inbound Router Advertisement and Router Redirect messages and drops them when they arrive on an access port, blocking rogue routers from advertising prefixes or becoming default gateways. This satisfies the requirement to prevent other routers' RAs from reaching hosts on that segment.
- ✗
The interface sends RAs with the autonomous flag set to allow SLAAC.
Why it's wrong here
The no-autoconfig flag clears the autonomous bit in advertised prefixes, so hosts cannot form addresses via SLAAC; RAs are still sent. It is tempting because the interface does emit RAs, and would be correct if autonomous addressing were intended rather than disabled.
- ✗
The interface only allows RAs from a specific authorized router.
Why it's wrong here
RAguard filters inbound Router Advertisements on access ports; it does not restrict them to one authorised router, which requires a different mechanism. It is tempting because raguard concerns RAs, and would be correct for blocking rogue RA senders, not for permitting a single trusted router.
- ✗
The interface drops all Neighbor Solicitations.
Why it's wrong here
RAguard inspects Router Advertisements; Neighbor Solicitations are unaffected and continue to be processed for address resolution. It is tempting because raguard filters ND traffic, and would be correct for suppressing rogue RAs, not for dropping all Neighbor Solicitation messages.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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