350-501 Networking Practice Question
Which statement about the use of MTU in an MPLS network is correct?
⚠ Common exam trap
Watch out — candidates often assume MPLS labels are part of the IP header (like an option) or that MPLS inherently handles fragmentation, when in fact the label is a separate shim that increases frame size and can cause MTU-related drops.
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
✓
MPLS adds a label stack to packets, reducing the payload MTU.
MPLS adds a label stack (typically 4 bytes per label) between the Layer 2 header and the IP packet. This additional overhead reduces the maximum payload size that can be carried without exceeding the interface MTU, effectively lowering the payload MTU available for the IP packet.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
MPLS adds a label stack to packets, reducing the payload MTU.
Why this is correct
The label overhead reduces available MTU for data.
- ✗
MPLS does not affect the MTU because labels are part of the header.
Why it's wrong here
Labels are additional headers that increase packet size.
- ✗
MTU must be increased on all MPLS interfaces.
Why it's wrong here
Not required; can use path MTU discovery.
- ✗
MPLS eliminates the need for IP fragmentation.
Why it's wrong here
Fragmentation may still occur.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.