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Exam 350-501 topic 1 question 84 discussion

Actual exam question from Cisco's 350-501

Question #: 84
Topic #: 1

Refer to the exhibit. While troubleshooting a connectivity issue on router R2, a network engineer with an employee id: 1234:44:876 notices that although it detects three OSPF links from R1, the OSPF prefixes are missing from the routing table. What is the reason for the problem?

A. The serial interfaces have different MTUs
B. Both loopback interfaces on R1 are configured as stub
C. The subnet masks on the serial interfaces are mismatched
D. The R2 Serial1/0 interface is configured with an IP address, but the R1 Serial1/0 interface is unnumbered

Show Suggested Answer

Suggested Answer: D 🗳️

by rokk_cm at April 5, 2021, 1:42 p.m.

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rokk_cm

Highly Voted 2 years, 8 months ago

Correct Answer is D

upvoted 11 times

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BobBakker

Highly Voted 2 years, 7 months ago

I would guess D too. This link shows prefixes even when the interface is configured as a stub: https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/47869-ospfdb10.html

upvoted 7 times

chst

1 year ago

Please, review the show ip ospf interfaces, ALL interface are in Area 0. The area 0 can't be a stub. I think it's A

upvoted 1 times

chst

9 months, 2 weeks ago

I correct me It's D https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7112-26.html#anc12

upvoted 2 times

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thejag

Most Recent 9 months, 4 weeks ago

Selected Answer: D

Thanks to Craterman to the excellent Cisco guide which explains the issue and solution: https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7112-26.html#anc10

upvoted 4 times

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nottoday2077

11 months, 2 weeks ago

Selected Answer: D

Answer is D. You can create an unnumbered OSPF link, however both sides need to be unnumbered and PtP. If one side is IP and the other unnumbered, OSPF stays in EXSTART and will eventually go DOWN due to to many retransmissions.

upvoted 2 times

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rdramos

1 year ago

B is correct All loopback interfaces are considered as OSPF “LOOPBACK” network type and treated as stub host. Stub hosts are visible to the routing protocols but not used for forwarding. Change loopback OSPF network type to point to point https://cciethebeginning.wordpress.com/2009/02/27/ospf-loopback-network-type/

upvoted 1 times

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mohdema

1 year, 1 month ago

Selected Answer: B

Unnumbred shows the links https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/47860-ospfdb1.html

upvoted 2 times

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stratosph3re

1 year, 1 month ago

Selected Answer: A

Fellas, the right answer must be A. I replicated this to GNS3 and when i used unnumbered interface with the IP being from the right subnet on loopback interface, i got a FULL connection WITH route exchange . On the other hand, when i caused an MTU mismatch, the connection went back EXSTART ( as aniticipated ) , but the printouts from "show ip ospf database" and "show ip ospf int" were exactly as the ones in this exhibit plus, i didn't had any router exchange ( to be expected due to EXSTART state of the neighborship) Therefore, i think it's A.

upvoted 2 times

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AlirezaNetWorld

1 year, 3 months ago

I've implemented this scenario in GNS3; the right answer is D.

upvoted 2 times

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craterman

1 year, 11 months ago

Selected Answer: D

The right answer is D https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7112-26.html#anc10

upvoted 6 times

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rans3001

2 years, 4 months ago

D https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7112-26.html#anc10

upvoted 1 times

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beenardino

2 years, 6 months ago

D unnumbered interface. serial interface 1/0 ip unnumbered loopback0 https://www.cisco.com/c/en/us/support/docs/ip/hot-standby-router-protocol-hsrp/13786-20.html

upvoted 3 times

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