Quick Answer
The correct answer is Penultimate Hop Popping (PHP), the MPLS forwarding mechanism that enables a core router to forward packets without checking the IP header. PHP works by having the penultimate hop router—the router just before the egress Label Switch Router (LSR)—pop the top label from the MPLS stack, so the egress router receives only the IP packet and can forward it based on the IP header or perform a simple layer-2 lookup. This eliminates the need for the egress router to perform two lookups (label and IP), streamlining the forwarding plane. On the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, this concept tests your understanding of MPLS label operations and the distinction between PHP and explicit null labels. A common trap is confusing PHP with CEF, but remember: CEF is IP-based, while PHP is label-only. For a quick memory tip, think “PHP = Pop Here, Please”—the penultimate hop does the popping so the final hop doesn’t have to.
This 350-501 practice question tests your understanding of architecture. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
An engineer needs to ensure that a core router can forward MPLS packets without checking the IP header. Which forwarding mechanism should be enabled?
Link Fragmentation and Interleaving (LFI)
Why wrong: LFI is for serialization delay, not MPLS forwarding.
CEF switching
Why wrong: CEF uses IP forwarding information.
Per-packet load balancing
Why wrong: Load balancing unrelated to label-only forwarding.
Penultimate Hop Popping (PHP)
PHP pops label at penultimate hop, so last hop forwards without IP check.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Penultimate Hop Popping (PHP)
Option B is correct because Penultimate Hop Popping (PHP) removes the label before the final hop, allowing forwarding based on label only. Option A is wrong because CEF is IP-based. Option C is wrong because LFI is for link fragmentation and interleaving. Option D is wrong because load balancing is distribution, not label-only.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Link Fragmentation and Interleaving (LFI)
Why it's wrong here
LFI is for serialization delay, not MPLS forwarding.
CEF switching
Why it's wrong here
CEF uses IP forwarding information.
Per-packet load balancing
Why it's wrong here
Load balancing unrelated to label-only forwarding.
Penultimate Hop Popping (PHP)
Why this is correct
PHP pops label at penultimate hop, so last hop forwards without IP check.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the 350-501 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Identify which 350-501 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Architecture — study guide chapter
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Architecture practice questions
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Cisco SPCOR / CCNP Service Provider Core 350-501 study guide
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350-501 practice test guide
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FAQ
Architecture — This question tests Architecture — Read the scenario before looking for a memorised answer..
The correct answer is: Penultimate Hop Popping (PHP) — Option B is correct because Penultimate Hop Popping (PHP) removes the label before the final hop, allowing forwarding based on label only. Option A is wrong because CEF is IP-based. Option C is wrong because LFI is for link fragmentation and interleaving. Option D is wrong because load balancing is distribution, not label-only.
Identify which 350-501 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This 350-501 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 350-501 exam.
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