The answer is the MPLS label stack with a control word for Ethernet frames. This encapsulation is correct because EVPN over MPLS uses a two-label stack—an inner VPN label for the EVPN instance and an outer transport label for MPLS forwarding—while the control word prevents packet misordering and ensures frame integrity across the MPLS network. On the Cisco SPCOR 350-501 exam, this question tests your understanding of the EVPN MPLS data plane, specifically how Ethernet frames are encapsulated rather than IP-tunneled or VLAN-tagged. A common trap is confusing the control plane (EVPN itself) with the data plane encapsulation, or assuming IP tunneling applies to MPLS-based EVPN. Remember the memory tip: “Control word keeps the Ethernet herd in order,” highlighting that the control word is essential for maintaining frame sequence in an MPLS label stack.
350-501 Architecture Practice Question
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.
A service provider is implementing EVPN with MPLS data plane. Which encapsulation type is used in MPLS EVPN to carry Ethernet frames across the MPLS network?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
MPLS label stack with a control word for Ethernet frames
EVPN over MPLS uses the MPLS label encapsulation with a control word. Option C is correct. Option A is wrong because Ethernet VLAN tagging is part of the frame. Option B is wrong because IP tunneling is used in EVPN with IP encapsulation. Option D is wrong because EVPN itself is the control plane.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Ethernet over MPLS (EoMPLS) with VLAN encapsulation
Why it's wrong here
EoMPLS is an older technology; EVPN uses MPLS labels with a control word.
✓
MPLS label stack with a control word for Ethernet frames
Why this is correct
The control word is used to preserve the Ethernet frame integrity.
Related concept
Access ports place end devices into a single VLAN.
✗
EVPN encapsulation defined by IETF RFC 7432
Why it's wrong here
RFC 7432 defines the control plane, not data plane encapsulation details.
✗
IP/MPLS tunnel with Ethernet frame inside
Why it's wrong here
EVPN over MPLS does not use IP tunnels; it uses MPLS label stacking.
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
Access ports place end devices into a single VLAN.
Trunk ports carry multiple VLANs between switches.
Allowed VLAN lists decide which VLANs can cross a trunk.
Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
→Use show vlan brief to verify access VLANs.
→Use show interfaces trunk to verify trunk state and allowed VLANs.
→Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
Got this wrong? Here's your next step.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 350-501 questions on switching, trunking, and access-port configuration.
Architecture — This question tests Architecture — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: MPLS label stack with a control word for Ethernet frames — EVPN over MPLS uses the MPLS label encapsulation with a control word. Option C is correct. Option A is wrong because Ethernet VLAN tagging is part of the frame. Option B is wrong because IP tunneling is used in EVPN with IP encapsulation. Option D is wrong because EVPN itself is the control plane.
What should I do if I get this 350-501 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 350-501 questions on switching, trunking, and access-port configuration.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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