- A
The interface is configured as an SD-WAN tunnel interface with color biz-internet, allowing DHCP, DNS, and ICMP traffic but blocking BGP.
This accurately describes the configuration: tunnel-interface enables SD-WAN, color sets the transport, and allow-service controls permitted protocols.
- B
The interface is configured as a standard WAN interface with IPsec encryption, allowing all services including BGP.
Why wrong: The 'no allow-service bgp' explicitly blocks BGP, so this is incorrect. Also, 'tunnel-interface' is specific to SD-WAN, not standard WAN.
- C
The configuration enables the interface as a loopback tunnel for OMP traffic only, blocking all other services.
Why wrong: This is incorrect because the interface is a physical GigabitEthernet interface, not a loopback. Also, DHCP, DNS, and ICMP are allowed, so not all services are blocked.
- D
The interface is configured for SD-WAN with color biz-internet, but the 'no allow-service bgp' command is invalid on a tunnel interface.
Why wrong: The 'no allow-service bgp' command is valid on a tunnel-interface; it explicitly denies BGP traffic through the tunnel.
Quick Answer
The correct answer is that the interface is configured as an SD-WAN tunnel interface with color biz-internet, allowing DHCP, DNS, and ICMP traffic while blocking BGP. This is because the `tunnel-interface` command places the GigabitEthernet into SD-WAN tunnel mode, and the `allow-service` and `no allow-service` directives explicitly filter which control-plane services are permitted over that tunnel—here, BGP is denied while DHCP, DNS, and ICMP are allowed. On the ENCOR 350-401 exam, this configuration tests your understanding of SD-WAN tunnel-interface allow-service control, often appearing in a multiple-choice scenario where you must identify which services are permitted or denied based on the snippet. A common trap is assuming that all services are allowed by default, but remember that `no allow-service bgp` explicitly overrides that default. Memory tip: think of the tunnel as a bouncer—only services on the “guest list” (DHCP, DNS, ICMP) get in, while BGP is turned away at the door.
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.
Consider the following SD-WAN configuration snippet on a Cisco IOS-XE router:
interface GigabitEthernet0/0/1 ip address 10.1.1.1 255.255.255.0
tunnel-interface
encapsulation ipsec
color biz-internet
no allow-service bgp
allow-service dhcp allow-service dns allow-service icmp !
What is the effect of this configuration?
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
The interface is configured as an SD-WAN tunnel interface with color biz-internet, allowing DHCP, DNS, and ICMP traffic but blocking BGP.
The configuration applies to a GigabitEthernet interface that is placed into SD-WAN tunnel mode using the 'tunnel-interface' command. The 'color biz-internet' assigns the transport color, and the 'allow-service' and 'no allow-service' commands explicitly control which control-plane services are permitted over the tunnel. DHCP, DNS, and ICMP are allowed, while BGP is explicitly denied, making option A correct.
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.
- ✓
The interface is configured as an SD-WAN tunnel interface with color biz-internet, allowing DHCP, DNS, and ICMP traffic but blocking BGP.
Why this is correct
This accurately describes the configuration: tunnel-interface enables SD-WAN, color sets the transport, and allow-service controls permitted protocols.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The interface is configured as a standard WAN interface with IPsec encryption, allowing all services including BGP.
Why it's wrong here
The 'no allow-service bgp' explicitly blocks BGP, so this is incorrect. Also, 'tunnel-interface' is specific to SD-WAN, not standard WAN.
- ✗
The configuration enables the interface as a loopback tunnel for OMP traffic only, blocking all other services.
- ✗
The interface is configured for SD-WAN with color biz-internet, but the 'no allow-service bgp' command is invalid on a tunnel interface.
Why it's wrong here
The 'no allow-service bgp' command is valid on a tunnel-interface; it explicitly denies BGP traffic through the tunnel.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that 'no allow-service bgp' is invalid or that the tunnel-interface configuration only applies to loopback interfaces, when in fact it is a valid command applied to physical interfaces to filter control-plane traffic per transport color.
Trap categories for this question
Command / output trap
The 'no allow-service bgp' command is valid on a tunnel-interface; it explicitly denies BGP traffic through the tunnel.
Detailed technical explanation
How to think about this question
In Cisco SD-WAN, the 'allow-service' and 'no allow-service' commands under 'tunnel-interface' control which control-plane protocols (e.g., BGP, OSPF, DHCP, DNS, ICMP) are permitted to traverse the tunnel for overlay management. By default, all services are allowed, so 'no allow-service bgp' explicitly blocks BGP peering over that transport color. This is commonly used in multi-color deployments to restrict BGP from using a specific transport (e.g., a backup or low-bandwidth link) while allowing essential services like DHCP and DNS for remote site provisioning.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
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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: The interface is configured as an SD-WAN tunnel interface with color biz-internet, allowing DHCP, DNS, and ICMP traffic but blocking BGP. — The configuration applies to a GigabitEthernet interface that is placed into SD-WAN tunnel mode using the 'tunnel-interface' command. The 'color biz-internet' assigns the transport color, and the 'allow-service' and 'no allow-service' commands explicitly control which control-plane services are permitted over the tunnel. DHCP, DNS, and ICMP are allowed, while BGP is explicitly denied, making option A correct.
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
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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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