Check the label on a router and see the following results: Which of the following statements is correct?

Question

Options

• AWhen sending a data packet whose destination address is 3.3.3.3, label 10 will be used and sent it.
• BWhen sending a data packet whose destination address is 4.4.4.4, send it directly without labeling.
• CWhen the router receives a packet with a label of 1024, it will change the label to 1027 and send it.
• DWhen forwarding data packet whose destination address is 2.2.2.2, send it directly without labeling.

• A
  2% (1)
• B
  6% (3)
• C
  8% (4)
• D
  85% (44)

Explanation

Option D is correct because in MPLS (Multi-Protocol Label Switching), when a router is the egress LSR (Label Switch Router) - meaning the destination (2.2.2.2) is directly reachable from it - the router forwards the packet as a plain IP packet with no label, a mechanism known as Implicit NULL or label popping.

Why the distractors are wrong:

• A is wrong because the table's entry for 3.3.3.3 does not specify label 10 as the outgoing label - the label value or action stated doesn't match the actual LFIB entry.
• B is wrong because 4.4.4.4 is not a directly connected destination on this router, so a label must be applied before forwarding - it cannot be sent unlabeled.
• C is wrong because receiving a packet with label 1024 triggers a pop (label removal) or a swap to a different label than 1027 - the described swap operation doesn't match what the LFIB table shows.

Memory tip: Think of the egress router as the "exit door" - once you're at the exit, you don't need your ticket (label) anymore. If the destination IP is directly attached to the router, the label gets stripped and the packet exits as plain IP. When in doubt on MPLS questions, ask: "Is this router the last hop?" - if yes, no label goes out.

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