- A
Both interfaces are in VPN 0, which is the transport VPN, and they will establish tunnels with the vSmart controller.
VPN 0 is the transport VPN in SD-WAN. Tunnel interfaces in VPN 0 are used to establish connections to the vSmart and vBond controllers.
- B
The interfaces are in VPN 0, which is the service VPN, and they will be used for customer traffic.
Why wrong: VPN 0 is the transport VPN, not the service VPN. Service VPNs are VPN 1-512 and are used for customer traffic.
- C
The configuration is invalid because tunnel interfaces cannot have IP addresses in the same VPN.
Why wrong: Tunnel interfaces can have IP addresses in VPN 0; these are the transport IP addresses used for overlay communication.
- D
The 'allow-service all' command is not supported on vEdge routers.
Why wrong: The 'allow-service all' command is supported on vEdge routers for tunnel interfaces.
350-401 SD-WAN Architecture Practice Question
This 350-401 practice question tests your understanding of sd-wan architecture. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Examine the following SD-WAN configuration on a Cisco vEdge router:
vpn 0
interface ge0/0 ip address 10.0.0.1/24
tunnel-interface
encapsulation ipsec
color public-internet allow-service all !
interface ge0/1 ip address 10.0.0.2/24
tunnel-interface
encapsulation ipsec
color 3g allow-service all !
Which statement is correct?
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
Both interfaces are in VPN 0, which is the transport VPN, and they will establish tunnels with the vSmart controller.
VPN 0 is the transport VPN in Cisco SD-WAN, used exclusively for underlay network connectivity and control plane traffic. The two interfaces ge0/0 and ge0/1 are configured as tunnel interfaces with IPsec encapsulation and different colors (public-internet and 3g), which allows them to establish secure DTLS/TLS tunnels to the vSmart controller for orchestration and policy distribution. This is correct because transport VPN interfaces are designed to carry overlay control traffic, not customer data.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Both interfaces are in VPN 0, which is the transport VPN, and they will establish tunnels with the vSmart controller.
Why this is correct
VPN 0 is the transport VPN in SD-WAN. Tunnel interfaces in VPN 0 are used to establish connections to the vSmart and vBond controllers.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The interfaces are in VPN 0, which is the service VPN, and they will be used for customer traffic.
Why it's wrong here
VPN 0 is the transport VPN, not the service VPN. Service VPNs are VPN 1-512 and are used for customer traffic.
- ✗
The configuration is invalid because tunnel interfaces cannot have IP addresses in the same VPN.
Why it's wrong here
Tunnel interfaces can have IP addresses in VPN 0; these are the transport IP addresses used for overlay communication.
- ✗
The 'allow-service all' command is not supported on vEdge routers.
Why it's wrong here
The 'allow-service all' command is supported on vEdge routers for tunnel interfaces.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that VPN 0 is a service VPN or that multiple tunnel interfaces in the same VPN are invalid, but the key is remembering that VPN 0 is strictly the transport underlay and supports multiple colored interfaces for control-plane connectivity.
Trap categories for this question
Command / output trap
The 'allow-service all' command is supported on vEdge routers for tunnel interfaces.
Detailed technical explanation
How to think about this question
Under the hood, each tunnel interface in VPN 0 uses a unique color (e.g., public-internet, 3g) to identify the transport circuit type, and the vEdge router builds separate IPsec tunnels per color to the vSmart and vBond controllers. The 'allow-service all' command enables essential control protocols like OMP (port 12346), BFD (port 3784), and Netconf (port 830) on the transport interface, which are critical for overlay operation. In a real-world deployment, multiple transport interfaces with different colors allow SD-WAN to perform active-active path selection and automatic failover based on SLA policies.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 350-401 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
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 350-401 question test?
SD-WAN Architecture — This question tests SD-WAN Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Both interfaces are in VPN 0, which is the transport VPN, and they will establish tunnels with the vSmart controller. — VPN 0 is the transport VPN in Cisco SD-WAN, used exclusively for underlay network connectivity and control plane traffic. The two interfaces ge0/0 and ge0/1 are configured as tunnel interfaces with IPsec encapsulation and different colors (public-internet and 3g), which allows them to establish secure DTLS/TLS tunnels to the vSmart controller for orchestration and policy distribution. This is correct because transport VPN interfaces are designed to carry overlay control traffic, not customer data.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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 →
Last reviewed: Jun 24, 2026
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.
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