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Exam 300-410 topic 1 question 499 discussion

Actual exam question from Cisco's 300-410

Question #: 499
Topic #: 1

Refer to the exhibit. After an engineer modified the configuration for area 7 to permit type 1, 2, and 7 LSAs only, users connected to router R9 reported that they could no longer access the internet. Which configuration restores internet access to users on R9 and permits only LSA type 1, 2, and 7?

A. R4#
router ospf 1
area 0 nssa default-information-originate
network 10.5.1.0 0.0.0.3 area 0
network 10.8.2.0 0.0.0.3 area 7

R9#
router ospf 1
area 7 nssa
redistribute eigrp 10 subnets
network 10.8.2.0 0.0.0.3 area 7
B. R4#
router ospf 1
area 7 nssa no-summary
network 10.5.1.0 0.0.0.3 area 0
network 10.8.2.0 0.0.0.3 area 7

R9#
router ospf 1
area 7 nssa
redistribute eigrp 10 subnets
network 10.8.2.0 0.0.0.3 area 7
C. R4#
router ospf 1
area 7 nssa
network 10.5.1.0 0.0.0.3 area 0
network 10.8.2.0 0.0.0.3 area 7

R9#
router ospf 1
area 7 nssa
redistribute eigrp 10 subnets
network 10.8.2.0 0.0.0.3 area 7
D. R4#
router ospf 1
area 0 area 7 stub no-summary
network 10.5.1.0 0.0.0.3 area 0
network 10.8.2.0 0.0.0.3 area 7

R9#
router ospf 1
area 7 stub
redistribute eigrp 10 subnets
network 10.8.2.0 0.0.0.3 area 7

Show Suggested Answer

Suggested Answer: B 🗳️

by b8os5h at Nov. 11, 2023, 11:12 a.m.

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[Removed]

10 months, 2 weeks ago

Selected Answer: B

B is corerct

upvoted 1 times

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bk989

1 year, 2 months ago

Answer is A according to this: This is a great question and sorry for the delayed response. For a NSSA that is not Totally Stubby, there is no default route originated by the ABR by default, but I think you know that already :slight_smile: When we use the no-summary technique on the ABR, a network summary LSA (Type 3) is produced and this propagates into the NSSA and is seen as an inter-area (IA) route. When we use default-route-originate on the ABR, a type 7 LSA is generated, so these will be regarded as External Routes. (Remember we have to use a Type 7 as Type 5s are being filtered due to the Area being stubby.) https://forum.networklessons.com/t/ospf-nssa-def-info-or-vs-no-summary-def-route/1567

upvoted 1 times

bk989

1 year, 2 months ago

Nevermind. Answer is B. The diagram cleartly shows internet as a default route.

upvoted 2 times

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ZamanR

1 year, 5 months ago

B Explanation Option B configures area 7 as a not-so-stubby area (NSSA) with the no-summary option on the area border router (ABR) R4. This allows the injection of external routes from EIGRP into the OSPF domain as type 7 LSAs, while preventing the propagation of inter-area summary LSAs into area 7. The no-summary option also generates a default summary route for area 7, which can be used by R9 to reach the internet2. Option A configures area 7 as a stub area, which does not allow any external routes or type 7 LSAs in the area. This prevents R9 from learning the EIGRP routes and accessing the internet3.

upvoted 4 times

ZamanR

1 year, 5 months ago

Option C configures area 7 as a NSSA without the no-summary option on R4. This allows the injection of type 7 LSAs into the area, but also allows the propagation of inter-area summary LSAs into the area. However, this option does not generate a default summary route for area 7, which means R9 has no route to reach the internet4. Option D configures area 7 as a NSSA with the default-information originate option on R4. This allows the injection of type 7 LSAs into the area, but also allows the propagation of inter-area summary LSAs into the area. The default-information originate option generates a type 7 default route for area 7, which can be used by R9 to reach the internet. However, this option is redundant and less efficient than Option B, because it injects both a type 3 and a type 7 LSA for the default route into the area5.

upvoted 4 times

Pietjeplukgeluk

1 year, 2 months ago

The reasoning why D is wrong seems inaccurate. the command "area 0 area 7 stub no-summary" in answer D seems incorrect. Futhermore the fact that D configures area 7 as stub instead of NSSA is considered "wrong" as the question clearly states to allow type 7 LSAs, this would not be possible with "stub" type.

upvoted 3 times

bk989

9 months, 2 weeks ago

He meant A and not D

upvoted 2 times

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bk989

9 months, 2 weeks ago

A or C works. Advantage of C is it makes less LSA SPF calculations in area 7. That's about it. But if I had to choose one for the exam i would choose C. C was specifically set uop for this type of situation.

upvoted 1 times

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[Removed]

1 year, 4 months ago

Excellent explanation.

upvoted 1 times

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AlexInShort12

1 year, 5 months ago

Selected Answer: B

Missing configuration in B answer area 7 nssa -> no-summary

upvoted 3 times

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b8os5h

1 year, 6 months ago

Selected Answer: B

A.NSSA (If the command is "area 7 nssa default-information-originate") B.Totally NSSA NSSA blocks LSA types 4 and 5 Totally NSSA blocks LSA types 3, 4, and 5 In NSSA, ABR does not automatically advertise a default route. Therefore, the "default-informationoriginate" keyword must be configured while configuring NSSA. In the case of Totally NSSA, there is no need to configure "default-information originate" to advertise the default route.

upvoted 4 times

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