Which ACL permits OSPF type 5 LSAs for 132.108.2.0 and .3.0?

300-410 By islever Editorial Last updated

Troubleshoot OSPF (v2/v3)

Short answer

A Access-list 1 permit 132.108.0.0 0.0.3.255 permits the range covering both 132.108.2.0/24 and 132.108.3.0/24 so their OSPF type 5 external LSAs are allowed.

Question

Refer to the exhibit. The R1 OSPF neighbor is not receiving type 5 external LSAs for 132.108.2.0/24 and 132.108.3.0/24 networks. Which configuration command resolves the issue? - Exhibit: Which ACL permits OSPF type 5 LSAs for 132.108.2.0 and .3.0?
  1. access-list 1 permit 132.108.0.0 0.0.3.255 Correct Answer
  2. access-list 1 permit 132.108.0.0 0.0.1.255
  3. access-list 1 permit 132.108.4.0 0.0.3.255
  4. access-list 1 permit 132.108.2.0 0.0.0.255

Key Takeaways

This item tests ACL wildcard-mask math for OSPF external LSA filtering; the trap is picking a mask that covers only 132.108.2.0/24 or the wrong 132.108.4.0 block.

R1 is missing OSPF type 5 external LSAs for 132.108.2.0/24 and 132.108.3.0/24 because the filtering ACL does not cover both prefixes. This page establishes that access-list 1 permit 132.108.0.0 0.0.3.255 (option A) is the command that permits the full 132.108.0.0–132.108.3.255 range.

Common mistake: A frequent wrong choice is D, because it permits 132.108.2.0/24 but leaves 132.108.3.0/24 filtered; C is also tempting but matches 132.108.4.0–132.108.7.255 instead.

Expert Analysis

Why the Answer Is Correct

A is correct because option A's wildcard mask 0.0.3.255 expands the ACL to cover 132.108.0.0 through 132.108.3.255, which includes both missing networks: 132.108.2.0/24 and 132.108.3.0/24. In an OSPF distribute-list scenario, the ACL must match the network addresses of the external LSAs that should be allowed; if either prefix is outside the permit range, R1 never receives its type 5 LSA. Because A includes both external subnets while no narrower or offset entry does, it is the only command that resolves the reported loss. The community consensus is unanimous on this, with alexnadal99 calling A "the only possible option."

Why the Other Options Are Wrong

Option B covers only 132.108.0.0–132.108.1.255, so neither 132.108.2.0/24 nor 132.108.3.0/24 is permitted. Option C uses 132.108.4.0 0.0.3.255, which matches the 132.108.4.0–132.108.7.255 range, the wrong side of the /22 boundary; as dancott put it, "C gives subnets.4.0 to.7.254". Option D permits exactly 132.108.2.0/24, so only one of the two type 5 LSAs is allowed and 132.108.3.0/24 remains missing. Thus B, C, and D each fail to include both advertised external networks.

Community Comment Notes

Several voters independently validated the range math. dancott and Commando1664 both noted that option C points to the.4.0–.7.255 block rather than the needed.0.0–.3.255 range. alexnadal99 described A as "the only possible option," and Chiaretta simply agreed that "A is right." Pietjeplukgeluk and Defilet also voted A, reinforcing that the community sees no ambiguity here.

Official Reference

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/command/iro-cr-book.html

This link opens the official vendor documentation in a new tab.

Exam Strategy

For ACL filtering questions, immediately translate the wildcard mask into a first-and-last address range before comparing options. Here only 0.0.3.255 covers both 132.108.2.0/24 and 132.108.3.0/24, while 0.0.0.255 covers just one of them.

Frequently Asked Questions

Why does access-list 1 permit 132.108.2.0 0.0.0.255 not solve the issue?

It permits only 132.108.2.0/24, so the type 5 LSA for 132.108.3.0/24 still does not match the ACL.

How does wildcard 0.0.3.255 cover both 132.108.2.0 and 132.108.3.0?

The wildcard range is 132.108.0.0–132.108.3.255, which includes both the .2.0/24 and .3.0/24 external prefixes.

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Community Votes

A
100%

100% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 6 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 6

  1. dancott 👍 5 Answered A
    should be A C gives subnets .4.0 to .7.254
  2. alexnadal99 👍 4 Answered A
    It should be A. It is the only possible option. 132.108.0.0 --- 132.108.3.255
  3. Commando1664 👍 3 Answered A
    C gives 132.108.4.0-132.108.7.255 Should be A 132.108.0.0-132.108.4.255
  4. Defilet 👍 4 Answered A
    Select A as well.
  5. Chiaretta 👍 3 Answered A
    A is right
Show 1 more comment
  1. Pietjeplukgeluk 👍 2 Answered A
    vote a

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