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Exam 350-501 topic 1 question 24 discussion

Actual exam question from Cisco's 350-501

Question #: 24
Topic #: 1

Refer to the exhibit. A network engineer is configuring customer edge routers to finalize a L2VPN over MPLS deployment. Assume that the AToM L2VPN service that connects the two CEs is configured correctly on the service provider network.
Which action causes the solution to fail?

A. OSPF does not work with L2VPN services.
B. The routing protocol network types are not compatible.
C. A loopback with a /32 IP address has not been used.
D. The xconnect statement has not been defined.

Show Suggested Answer

Suggested Answer: B 🗳️

by KNOPPER at Oct. 1, 2020, 7:07 p.m.

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costascarramanlis

Highly Voted 4 years, 7 months ago

The correct answer is B. Why? First, In the question it clearly says that you have to assume the AToM is configured correctly. Secondly, clearly you see that the network type is not specified and the default types for ethernet is broadcast with DR whereas serial is point-to-point, these don't match.

upvoted 7 times

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ric859

Most Recent 7 months, 2 weeks ago

Selected Answer: B

D cannot be correct because it is stated that the configuration is on the CEs. The CEs on an L2VPN implementation will not have any xconnect configuration since they are agnostic to the transport that connects them. The OSPF adjacency between the two will not work because the default OSPF network type is different on a fastethernet and a serial interface.

upvoted 1 times

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wenzET

11 months ago

You need loopback to be configure in CE, so Answer is C https://community.cisco.com/t5/service-providers-knowledge-base/configuration-example-atom-any-transport-over-mpls-for-like-to/ta-p/3144810

upvoted 1 times

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sushil_bhattacharjee

1 year, 4 months ago

Selected Answer: B

Sorry, my previous understanding is wrong. Here, CE routers, and it doesn't do anything with xconnect; only PE does xconnect. Hence, D is wrong. OSPF works with L2VPN, hence A is wrong. OSPF can't build neighbour adjacency if there is a network type mismatch; hence, the correct answer is B.

upvoted 1 times

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ariasse

1 year, 4 months ago

Selected Answer: B

Agree with "sushil_bhattacharjee". Correct Answer should be "D".

upvoted 1 times

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sushil_bhattacharjee

1 year, 5 months ago

Selected Answer: D

For instance, it looks like [CE1<-->PE1<-->P1<-->P2<-->PE2<-->CE2] A. is not correct. Since OSPF works with L2VPN B. There is no neighbourship in between CE1 and CE2, rather it is CE1 with PE1 and CE2 with PE2. C. It is not mandatory to add loopback. So it is not correct. D. It requires to add the "xconnect" command under the interface in CE rotuers which are missing in the display. It requires to add under the interface command in the CE1 and CE2 "Router(config)# interface <interface-type>/<interface-number> Router(config-if)# xconnect <peer-address> <vc-id> encapsulation mpls". Therefore, Answer D is correct, in my opinion.

upvoted 2 times

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velozkenneth

3 years ago

Selected Answer: B

Both network types should be same

upvoted 1 times

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KNOPPER

4 years, 9 months ago

I think the correct answer is D. https://www.cisco.com/en/US/docs/ios/12_4t/mpls/configuration/guide/tpseudo.html#wp1054177

upvoted 1 times

EdgardoAC

4 years, 8 months ago

The Xconnect statement is required on the PE interface that faces the CE, both configurations shown are of CE routers, so Xconnect statement would not be relevant.

upvoted 7 times

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