The correct statement is that MPLS adds a label stack to packets, reducing the payload MTU. This is because each MPLS label adds four bytes of overhead per label in the stack, which consumes part of the maximum transmission unit of the underlying Layer 2 link. When a router imposes a label stack on an IP packet, the total frame size increases, so the original payload must be smaller to avoid exceeding the interface MTU; if the packet is already at the MTU limit, the extra label overhead forces fragmentation or drop. On the Cisco SPCOR 350-501 exam, this concept tests your understanding that MPLS does not magically increase MTU—it adds overhead, and the effective payload MTU shrinks. A common trap is assuming MPLS avoids fragmentation or that the MTU is automatically adjusted; instead, remember that label imposition reduces the room for data. Memory tip: “Labels eat bytes—payload shrinks by four per hop.”
350-501 Networking Practice Question
This 350-501 practice question tests your understanding of networking. 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.
Which statement about the use of MTU in an MPLS network is correct?
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.
Option C is correct. MPLS adds a label stack header, which reduces the effective MTU for payload. If the packet size exceeds the MTU of the outgoing interface after label imposition, fragmentation may be needed. Option A is false because MPLS can fragment (though not always desirable); Option B is false because MTU is not automatically increased; Option D is false because MPLS adds overhead.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Related concept
Static NAT maps one inside address to one outside address.
✗
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.
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-501 NAT questions on configuration and troubleshooting.
Networking — This question tests Networking — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: MPLS adds a label stack to packets, reducing the payload MTU. — Option C is correct. MPLS adds a label stack header, which reduces the effective MTU for payload. If the packet size exceeds the MTU of the outgoing interface after label imposition, fragmentation may be needed. Option A is false because MPLS can fragment (though not always desirable); Option B is false because MTU is not automatically increased; Option D is false because MPLS adds overhead.
What should I do if I get this 350-501 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-501 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.