hardMultiple Choice
350-401 Practice Question: Runs the following command on Router R2: R2# show…
A network engineer runs the following command on Router R2:
R2# show mpls forwarding-table
Local Outgoing Prefix Bytes Label Outgoing Next Hop Label Label or Tunnel Id Switched interface 16 Pop Label 10.1.1.1/32 0 Gi0/0 192.168.1.1 17 18 10.2.2.0/24 1500 Gi0/1 192.168.2.3 18 Untagged 10.3.3.0/24 0 Gi0/2 192.168.3.4
Based on this output, what is the correct interpretation?
⚠ Common exam trap
Cisco often tests the distinction between 'Pop Label' (PHP), 'Untagged' (egress or no label), and a numeric outgoing label (swap), and candidates commonly misinterpret 'Untagged' as meaning the label is removed or that a label is still present.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
For prefix 10.1.1.1/32, the router will pop the MPLS label before forwarding because the outgoing label is 'Pop Label'.
The 'Pop Label' entry in the 'Outgoing Label' column indicates that for the prefix 10.1.1.1/32, Router R2 is the penultimate hop (PHP) in the MPLS network. According to MPLS PHP behavior, the router will remove (pop) the top label from the MPLS packet before forwarding the IP packet to the next hop (192.168.1.1), which is the egress LSR.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
For prefix 10.1.1.1/32, the router will pop the MPLS label before forwarding because the outgoing label is 'Pop Label'.
Why this is correct
For the /32 prefix, the outgoing label is 'Pop Label', which signals Penultimate Hop Popping (PHP). The router, acting as the penultimate LSR, removes the MPLS label before forwarding the IP packet to the egress router, avoiding the need for the egress to perform a label lookup. This operation reduces processing overhead and is a common optimization in MPLS networks.
- ✗
For prefix 10.2.2.0/24, the router will impose label 18 onto the packet.
Why it's wrong here
The outgoing label for 10.2.2.0/24 is 18, but this represents a swap operation, not an imposition. An impose (or push) operation occurs only at the ingress LSR when adding a label to an unlabeled IP packet. Since the router already has label 17 on this incoming packet, it swaps that label to 18 and forwards it, so the claim of imposing a new label is incorrect.
- ✗
For prefix 10.3.3.0/24, the router will forward the packet with an MPLS label of 18.
Why it's wrong here
For 10.3.3.0/24, the forwarding table explicitly shows 'Untagged', meaning the packet is forwarded without any MPLS label. The router will send the packet as a plain IP packet, possibly after popping the label if it was labeled. Therefore, stating that it will forward with an MPLS label of 18 directly contradicts the 'Untagged' condition, making the statement false.
- ✗
The router has received 1500 bytes for prefix 10.2.2.0/24, and the outgoing interface is Gi0/1.
Why it's wrong here
The 'Bytes Label Switched' field counts the total accumulated bytes that have traversed the router using the specified incoming label, not the size of a single received packet. The value 1500 is a counter, so it does not indicate that a 1500-byte packet was just received for 10.2.2.0/24. While Gi0/1 is indeed the outgoing interface, the byte interpretation is invalid, making the statement incorrect.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.