Question 1,080 of 2,011
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300-410 Practice Question: Consider the following configuration: ipv6…
Consider the following configuration:
ipv6 access-list FILTER
permit ipv6 2001:db8:3::/48 any deny ipv6 any any interface GigabitEthernet0/5
ipv6 traffic-filter FILTER in ipv6 verify unicast source reachable-via rx
A packet arrives on GigabitEthernet0/5 with source 2001:db8:3::100 and destination 2001:db8:4::1. The route for 2001:db8:3::/48 points out interface GigabitEthernet0/6. What happens?
⚠ Common exam trap
Cisco often tests the order of operations: uRPF is checked before ACLs, so candidates mistakenly think the ACL permit will allow the packet, but uRPF drops it first.
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 packet is dropped by uRPF because strict mode requires the source to be reachable via the receiving interface.
The packet is dropped by uRPF (unicast Reverse Path Forwarding) in strict mode because the `ipv6 verify unicast source reachable-via rx` command checks that the source address 2001:db8:3::100 is reachable via the receiving interface (GigabitEthernet0/5). The route for the source prefix 2001:db8:3::48 points out GigabitEthernet0/6, not the receiving interface, so uRPF fails and drops the packet before the ACL is evaluated.
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 packet is permitted because the ACL matches and uRPF is not applied.
Why it's wrong here
uRPF is applied; both ACL and uRPF must pass.
- ✓
The packet is dropped by uRPF because strict mode requires the source to be reachable via the receiving interface.
Why this is correct
Strict uRPF (rx) fails because the return route uses a different interface.
- ✗
The packet is dropped by the ACL because the deny statement blocks all traffic.
Why it's wrong here
The permit statement matches the source prefix, so the ACL permits the packet.
- ✗
The packet is permitted because uRPF only checks destination addresses.
Why it's wrong here
uRPF checks the source address, not the destination.
Visual reference
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Last reviewed: Jul 4, 2026
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