Exam 350-501 topic 1 question 168 discussion

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.

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

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.

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.

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

Got this question in Exam.

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

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.