Refer to the exhibit. Router 1 is a P router in the ISP MPLS core. A connected P router cannot generate an MPLS label for the router 1 loopback0 interface. Which action resolves this issue?

Question

Options

• AThe loopback0 interface must be in OSPF area 0.
• BThe network statement under the routing process must have a wildcard mask of 0 0.0 255.
• CThe OSPF network type must be changed on loopback0 to point-to-point
• DA static route to null 0 must be added for the loopback interface and then static routes must be

• A
  8% (3)
• B
  56% (22)
• C
  23% (9)
• D
  13% (5)

Explanation

Option B is correct because MPLS label generation depends on LDP (Label Distribution Protocol) distributing labels for prefixes that exist in the routing table. If the OSPF network statement has an incorrect wildcard mask that doesn't match the loopback's IP address, the loopback won't be advertised into OSPF - meaning the neighboring P router never learns the route, so it cannot generate an MPLS label for it. A wildcard mask of 0.0.0.0 (exact match) ensures the specific loopback IP is correctly included in the OSPF domain and propagated to peers.

Why the distractors are wrong:

• A - Area placement matters for inter-area reachability, but the issue here is the loopback not being advertised at all due to the misconfigured network statement, not which area it's in.
• C - Changing the OSPF network type to point-to-point affects how the prefix mask is advertised (actual mask vs. host /32), but doesn't fix a loopback that isn't being advertised in OSPF at all.
• D - A static route to Null0 is used for route summarization or loop prevention; it's an overly complex workaround and isn't the appropriate fix for this label generation failure.

Memory tip: Think of it as a chain - "No OSPF advertisement → no route in neighbor's table → no LDP label." MPLS labels follow IGP routes, so always verify your network statement wildcard masks actually cover your loopback interfaces before troubleshooting LDP.

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