300-410 Practice Question: The default behavior of an IPv4 ACL regarding the…

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 most specific entry is used regardless of order.

  Why it's wrong here

  IPv4 ACLs evaluate entries sequentially from the top down, applying the first match and stopping; specificity plays no part in selection. This option tempts because longest-prefix-match governs routing lookups, where the most specific route wins regardless of configuration order — a genuine mechanism, but one belonging to the routing table rather than to ACL processing.

• ✓

  The first matching entry in the list is applied.

  Why this is correct

  IPv4 ACLs are evaluated top-down, and processing stops at the first entry whose criteria match the packet. Later entries, even if more specific, are never examined, so ordering entries correctly is essential to obtain the intended permit or deny result.

• ✗

  All matching entries are evaluated and the most permissive action is taken.

  Why it's wrong here

  Cisco IOS applies the first matching entry and stops processing, so later entries are never examined; there is no permissive-action aggregation. This tempts because firewall policy engines sometimes merge rules, but ACLs are strictly sequential, making first-match the operative mechanism.

• ✗

  The last matching entry in the list overrides earlier ones.

  Why it's wrong here

  IPv4 ACLs evaluate top-down and stop at the first match, so a later entry never overrides an earlier one. The temptation is that many list-processing systems apply last-match-wins semantics, and that ordering does hold for some other rule engines, but Cisco IOS ACLs commit to the first matching statement.