How to Make OSPF Area 1 Totally Stubby on R2

Troubleshoot OSPF (v2/v3)

Answer Correct answer: D — Configure area 1 stub no-summary on R2 to make area 1 totally stubby, so R3 sees only Type 1 and Type 2 LSAs.

Refer to the exhibit. An engineer must ensure that R3 sees only type 1 and 2 LSAs in area 1. Which command must the engineer apply on R2? -

area 1 nssa no-summary
area 1 stub
area 1 stub nssa
area 1 stub no-summary Correct Answer

Community Votes

76%

24%

76% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.

Community Insight

Tests the OSPF LSA filtering difference between stub, totally stubby, and NSSA areas; the trap is selecting area 1 stub because it blocks Type 4 and 5 LSAs but still floods Type 3 summaries into R3.

OSPF area 1 on R3 must see only Type 1 and Type 2 LSAs, which requires making it a totally stubby area from the ABR R2. This page confirms that the command area 1 stub no-summary (D) is correct, and explains why plain stub and NSSA options fail.

The most common wrong choice is B, area 1 stub, because many engineers assume stub already eliminates Type 3 LSAs; in reality only the no-summary keyword suppresses Type 3, Type 4, and Type 5 summaries.

Community Discussion (8 comments)

Sammy3637 👍 1 Selected: D

area 1 stub: Configures the area as a stub area, which only allows Type 1 (Router) and Type 2 (Network) LSAs, but it may still receive Type 3 (Summary) LSAs from other areas. no-summary: This command, when added to the configuration, prevents Type 3 (Summary), Type 4, and Type 5 (External) LSAs from being generated in a stub area. It ensures that only Type 1 and Type 2 LSAs are allowed into the area.

ANEE167 👍 1

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bk989 👍 3 Selected: D

Stub: type 1 2 3 LSA stub no summary --> allows Type 1 2 originated inside the stub area itself. default route (a single type 3 default route, that prevents type 3 inter-area routes) that points to type 1 2 3 LSA's on the outside of the stub area NSSA Type 1 2 3 7 LSA NSSA no-summary blocks inter-area routes. Gives 1 default route to outside of the NSSA. NSSA no-summary --> type 1 2 7 inside the area itself, one default route to inter-area and Type 5 external routes

[Removed] 👍 3 Selected: D

D is correct Stub Area without no-summary: "area 1 stub" alone will send LSA type 1, 2, 3 Stub Area with no-summary: "area 1 stub no-summary" explicitly prevents type 3 (summary) LSAs from being sent into the area. It´s essentially a more explicit configuration that confirms type 1 and type 2 LSAs are the only types allowed and also ensures that type 3 LSAs are not present.

[Removed] 👍 2 Selected: D

D is correct Stub Area without no-summary: "area 1 stub" alone prevents type 3 and type 5 LSAs from being received in the stub area. Stub Area with no-summary: "area 1 stub no-summary" explicitly prevents type 3 (summary) LSAs from being sent into the area. It´s essentially a more explicit configuration that confirms type 1 and type 2 LSAs are the only types allowed and also ensures that type 3 LSAs are not present.

dapardo 👍 4 Selected: B

stub No-Summary = totally stubby area

acg888 👍 4 Selected: D

coorecta

Comments & Corrections

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Expert Analysis

Why the Answer Is Correct

The requirement is for R3 to receive only Type 1 (router) and Type 2 (network) LSAs in area 1, which means the ABR R2 must stop flooding Type 3 summary, Type 4 ASBR-summary, and Type 5 external LSAs into that area. The Cisco command area 1 stub no-summary configures area 1 as a totally stubby area on R2. A plain stub area only blocks Type 4 and Type 5 LSAs, so R3 would still see Type 3 summaries; adding no-summary suppresses them. Although the ABR injects a default inter-area route, the only non-default LSAs R3 sees are Type 1 and 2. Thus D is the command to apply on R2.

Why the Other Options Are Wrong

A (area 1 nssa no-summary) creates a totally NSSA, which allows Type 7 LSAs and is intended for areas that inject external routes, so it does not meet the requirement of only Type 1 and 2 LSAs. B (area 1 stub) is a normal stub area and still permits Type 3 summary LSAs from R2. C (area 1 stub nssa) is an invalid combination because an area cannot be both stub and NSSA. D is the only option that makes area 1 totally stubby and filters out Type 3, 4, and 5 LSAs.

Community Comment Notes

The community strongly favors D, with dapardo noting "stub No-Summary = totally stubby area." bk989 correctly explains that plain stub allows Type 1, 2, and 3 LSAs, while no-summary removes the Type 3 summaries. Sammy3637 adds that no-summary prevents Type 3, Type 4, and Type 5 LSAs, leaving only Type 1 and 2. A few voters chose B, likely because they forgot that a normal stub area still receives Type 3 summary LSAs. acg888 simply marked D as correct.

Official Reference

https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7039-1.html

Exam Strategy

Remember that no-summary is configured on the ABR, while internal routers use plain area 1 stub; the question asks for R2, so choose the ABR command. Also map each area type to the LSA types it blocks: stub blocks 4 and 5, totally stubby blocks 3, 4, and 5, and NSSA blocks 4 and 5 but allows 7.

Frequently Asked Questions

Why does area 1 stub no-summary still allow a default route into R3?

The ABR still injects one Type 3 default summary LSA, but it suppresses all other Type 3, 4, and 5 LSAs, so R3's LSDB contains mainly Type 1 and 2 plus the default.

Why is area 1 nssa no-summary wrong for this requirement?

NSSA no-summary allows Type 7 LSAs and is for areas redistributing external routes, so it cannot restrict area 1 to only Type 1 and 2 LSAs.

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