This 350-401 practice question tests your understanding of vrf and path isolation. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 migrating a customer from a global routing table to a VRF on a Cisco ASR 1000. The customer has a BGP session with the provider for internet access. After moving the customer's interface to VRF CUSTOMER_D, the BGP session goes down. The engineer verifies that the VRF is configured with the correct route-target and that the BGP neighbor is configured under address-family ipv4 vrf CUSTOMER_D. What else is missing?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The IP address on the interface was removed when the VRF was applied, and it was not reconfigured.
When a VRF is applied to an interface on a Cisco ASR 1000, the interface's IP address is removed because the VRF changes the routing context. The engineer must reconfigure the IP address under the VRF interface. Without the IP address, the BGP session cannot establish a TCP connection, causing it to go down.
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 IP address on the interface was removed when the VRF was applied, and it was not reconfigured.
Why this is correct
Correct because the ip vrf forwarding command clears the IP address on the interface, requiring it to be re-entered.
Related concept
Read the scenario before looking for a memorised answer.
✗
The BGP neighbor is not configured with the password command.
Why it's wrong here
Incorrect because a password is not required for BGP to come up.
✗
The route-target import/export values are incorrect for the customer.
Why it's wrong here
Incorrect because route-targets affect VPNv4 route distribution, not the BGP session directly.
✗
The engineer forgot to configure the VRF under the BGP router-id.
Why it's wrong here
Incorrect because the router-id is global and not VRF-specific.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the fact that applying a VRF to an interface removes the IP address, leading candidates to overlook the need to reconfigure it, and instead focus on BGP or VRF configuration errors.
Detailed technical explanation
How to think about this question
Applying a VRF to an interface with the `ip vrf forwarding` command removes the Layer 3 IP address from the interface, as the VRF changes the routing table context. The engineer must reapply the IP address using `ip address` after the VRF is set. This behavior is specific to Cisco IOS-XE and ensures the interface belongs to the correct VRF before any IP configuration is accepted.
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 network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
VRF and Path Isolation — This question tests VRF and Path Isolation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The IP address on the interface was removed when the VRF was applied, and it was not reconfigured. — When a VRF is applied to an interface on a Cisco ASR 1000, the interface's IP address is removed because the VRF changes the routing context. The engineer must reconfigure the IP address under the VRF interface. Without the IP address, the BGP session cannot establish a TCP connection, causing it to go down.
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.
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Question Discussion
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