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Exam 350-501 topic 1 question 168 discussion

Actual exam question from Cisco's 350-501

Question #: 168
Topic #: 1

A regional MPLS VPN provider operates in two regions and wants to provide MPLS L3VPN service for a customer with two sites in these separate locations. The
VPN provider approaches another organization to provide backbone carrier services so that the provider can connect to these two locations.
Which statement about this scenario is true?

A. When edge routers at different regional sites are connected over the global carrier backbone, MP-eBGP must run between the routers to exchange the customer VPNv4 routes.
B. When eBGP is used for label exchange using the send-label option, MPLS-BGP forwarding is configured under the global ABC CSC PE-to-CE interface.
C. When BGP is used for both route and label exchange, the neighbor a.b.c.d send-label command is used under the address-family VPNv4 command mode.
D. When IGP is used for route exchange and LDP for label exchange, MPLS is enabled only on the VRF interface on the backbone-carrier PE side.

Show Suggested Answer

Suggested Answer: B 🗳️

by iliveinspace at June 28, 2020, 1:24 p.m.

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iliveinspace

Highly Voted 5 years ago

B is worded badly but is referring to "(int)#mpls bgp forwarding", which has the IOS[-XE] software install a hostroute for the remote BGP peer - a requirement for label-binding. B is therefore the most correct answer.

upvoted 9 times

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rans3001

Most Recent 1 year ago

Selected Answer: B

A is wrong, we need to run MP-iBGP between edge routers connected to the CSC service.

upvoted 2 times

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Mo_El

2 years, 2 months ago

Selected Answer: A

B is misleading; "mpls bgp forwarding" is configured between ASBRs not PE-CE. I pick A as for CSC options B and C; VPNv4 sessions between the different AS#s needed to exchange customers routes.

upvoted 1 times

Mo_El

2 years, 1 month ago

B is actually the correct one. A is wrong because same Provider edge devices will have to exchange iBGP vpnv4 not eBGP vpnv4.

upvoted 3 times

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mohdema

2 years, 8 months ago

Label Exchange Methods in CSC Architecture There are two ways of exchanging IGP labels in an MPLS VPN network: • Using IGP for label exchange • Using BGP for label exchange Using IGP for Label Exchange This method employs the traditional approach of using an IGP to exchange routes between PE-CE routers. Label exchange is performed using TDP/LDP protocols. Figure 8-2 shows the configuration steps for enabling MPLS on PE-CE routers. Using BGP for Label Exchange In this method, BGP is used for routing and for label exchange. When using EBGP for label exchange, mpls bgp forwarding is automatically configured under the interface. Prior to that, ensure that TDP/LDP Protocol (mpls ip) is not enabled on the interface. Figure 8-3 shows the steps to configure BGP for IPv4 label distribution.

upvoted 1 times

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serban_17

4 years ago

B seems kind of the right answer, but only because the other look rather wrong

upvoted 2 times

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nolbi

4 years ago

Got this question in Exam.

upvoted 1 times

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iliveinspace

5 years ago

C is incorrect as in CSC, the send-label neighbor config goes under IPv4 Unicast AFI

upvoted 1 times

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iliveinspace

5 years ago

Although D looks correct, "MPLS is enabled only on the VRF interface" is untrue as the carrier needs MPLS on its transit links to provide CSC transport. "Only" is the keyword that suggests D is incorrect.

upvoted 2 times

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