Solving AC Layer 2 Encapsulations Mismatch for MPLS L2VPN

D.

In this scenario, the network consultant has identified that the Attachment Circuit (AC) Layer 2 encapsulations are different, which means that the Layer 2 frames from the AC cannot be transported over the MPLS network as is. This situation requires the use of Layer 2 VPN services over MPLS, such as Any Transport over MPLS (AToM) to enable the transport of Layer 2 frames across the MPLS network.

The correct action to take in this scenario is to use interworking to ensure that the different Layer 2 encapsulations can be transported over the MPLS network. Interworking is the process of converting between different Layer 2 encapsulation types.

Option A, "tag-rewrite on the ingress and egress PE router," is incorrect because tag-rewrite only works for MPLS Layer 3 VPNs, not Layer 2 VPNs.

Option B, "interworking IP configuration on the last PE router before label disposition," is incorrect because it is not necessary to have an IP interworking configuration for a Layer 2 VPN service.

Option D, "interworking IP configuration on both the AC terminations on the PEs," is also incorrect because it is not necessary to configure IP interworking for a Layer 2 VPN service.

Therefore, the correct answer is C, "nonrouted interworking setup to properly translate only the Layer 2 information from the AC." Nonrouted interworking involves translating only the Layer 2 information from the AC, without any routing or IP encapsulation, to ensure that the Layer 2 frames can be transported across the MPLS network. This type of interworking is typically used for Ethernet-based services, such as Ethernet over MPLS (EoMPLS) or AToM.