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300-410 Practice Question: Runs the following command on Router R1: R1# show…

A network engineer runs the following command on Router R1:

R1# show ipv6 access-list PERMIT-ONLY

IPv6 access list PERMIT-ONLY

permit ipv6 2001:DB8:3::/48 any sequence 10

Based on this output, what is the effect of this access list when applied to an interface?

⚠ Common exam trap

Cisco often tests the implicit deny any any behavior in IPv6 ACLs, tricking candidates into thinking that a single permit entry allows all traffic or that the ACL only filters the specified prefix without affecting other traffic.

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

It permits only IPv6 traffic from 2001:DB8:3::/48 and denies everything else

An IPv6 access list, like its IPv4 counterpart, has an implicit deny all at the end. The single permit entry for source 2001:DB8:3::/48 allows only traffic from that prefix; all other IPv6 traffic is denied by the implicit deny ipv6 any any rule.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • It permits all IPv6 traffic

    Why it's wrong here

    Only traffic from the specified prefix is permitted; other traffic is implicitly denied.

  • It permits only IPv6 traffic from 2001:DB8:3::/48 and denies everything else

    Why this is correct

    The permit statement allows the prefix, and the implicit deny denies all other traffic.

  • It denies all IPv6 traffic from 2001:DB8:3::/48

    Why it's wrong here

    The ACL permits that prefix.

  • It permits all IPv6 traffic except from 2001:DB8:3::/48

    Why it's wrong here

    The ACL does the opposite – it permits that prefix and denies all else.

Visual reference

Source Router + ACL permit 10.0.0.0/8 deny any Server 10.0.0.5 ✓ 192.168.1.1 ✗ dropped ACLs evaluate top-down; first match wins — implicit deny all at end

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JA

Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

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