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300-410 Practice Question: In IPv6, what is the default action for an…
In IPv6, what is the default action for an access-list entry that does not specify a protocol?
⚠ Common exam trap
Cisco often tests the misconception that an ACE without a protocol defaults to 'permit ipv6' or 'deny ipv6', similar to how IPv4 ACLs handle missing protocol fields, but in IPv6 the entry is simply invalid and ignored.
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 ACE is invalid and ignored.
In IPv6, an access-list entry (ACE) that does not specify a protocol is considered invalid and is ignored by the router. This is because the IPv6 access-list syntax requires a protocol keyword (e.g., tcp, udp, icmp, or a protocol number) to define the match criteria; without it, the ACE cannot be parsed correctly and is treated as a configuration error, not a default permit or deny.
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 ACE defaults to 'permit ipv6'.
Why it's wrong here
There is no default protocol; the ACE must explicitly specify a protocol.
- ✓
The ACE is invalid and ignored.
Why this is correct
Cisco IOS requires a protocol in each IPv6 ACL entry; without it, the entry is invalid.
- ✗
The ACE defaults to 'deny ipv6'.
Why it's wrong here
No default protocol is assumed; the entry is simply invalid.
- ✗
The ACE matches all IPv6 traffic.
Why it's wrong here
Only the 'ipv6' keyword matches all IPv6 traffic; omitting the protocol makes the entry invalid.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.