Refer to the exhibit. The CE router has established a BGP peering with the PE router, and the CE will use the core infrastructure of the PE as a backbone carrier to support CSC. Which additional task

Question

Exhibit

Options

• AConfigure static routing on the CE router.
• BConfigure the address-family ipv4 labeled-unicast command under the neighbor configuration of
• CChange the rd value to 65001:65001 under the VRF section of the PE router.
• DConfigure OSPF on the PE router.

• A
  6% (2)
• B
  15% (5)
• C
  3% (1)
• D
  76% (25)

Explanation

In a Carrier Supporting Carrier (CSC) architecture, the PE router must participate in an IGP - such as OSPF - within the backbone carrier's network so that MPLS label distribution (via LDP) can function across the core. Without OSPF on the PE, labeled routes received from the CE cannot be propagated through the backbone, breaking the CSC transport service.

Why the distractors are wrong:

• A (Static routing on CE): CSC relies on dynamic BGP with labeled unicast exchanges between CE and PE, not static routes, which would not scale and would not carry MPLS labels.
• B (address-family ipv4 labeled-unicast on CE): While this is required in a CSC BGP configuration, the question states that BGP peering is already established, implying the necessary address families are in place; this is not the missing piece.
• C (Change RD to 65001:65001): Route Distinguisher values are locally significant and don't need to follow a specific format to make CSC work; changing the RD does not address the forwarding requirements of the backbone.

Memory tip: Think "CSC = IGP on PE first." The backbone carrier's PE must speak OSPF (or IS-IS) so LDP can distribute labels end-to-end through the core - no IGP, no labels, no CSC.

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