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 router has the following configuration snippet:
vrf definition RED
rd 100:1
!
interface Loopback0
ip vrf forwarding RED
ip address 10.0.0.1 255.255.255.255
!
router eigrp 100
address-family ipv4 unicast vrf RED autonomous-system 100
network 10.0.0.1 0.0.0.0
What is the issue with this EIGRP configuration for VRF RED?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The EIGRP address-family is not activated because 'no shutdown' is missing under the address-family configuration.
The EIGRP address-family configuration for VRF RED is missing the 'no shutdown' command under the address-family mode. In Cisco IOS, EIGRP address-families are administratively shut down by default; without 'no shutdown', the EIGRP process for that VRF will not form adjacencies or advertise routes, even though the network command is correctly configured.
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 EIGRP address-family is not activated because 'no shutdown' is missing under the address-family configuration.
Why this is correct
Correct. EIGRP address-families require 'no shutdown' to start.
Related concept
Read the scenario before looking for a memorised answer.
✗
The 'network' command should use a wildcard mask of 0.0.0.255 instead of 0.0.0.0.
Why it's wrong here
Incorrect. A host mask is valid for a loopback interface.
✗
The VRF must be defined under 'router eigrp' globally before using address-family.
Why it's wrong here
Incorrect. The address-family vrf command is the correct method.
✗
The loopback interface cannot be placed in a VRF because it is a virtual interface.
Why it's wrong here
Incorrect. Loopback interfaces can be placed in VRFs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the default administrative shutdown of EIGRP address-families, knowing that many candidates assume the process starts automatically once the network command is configured, leading them to overlook the required 'no shutdown' command.
Trap categories for this question
Command / output trap
Incorrect. The address-family vrf command is the correct method.
Detailed technical explanation
How to think about this question
EIGRP named mode address-families are administratively shutdown by default to prevent accidental route leaks or adjacency formation before the configuration is complete. This behavior differs from classic EIGRP, where the router process starts immediately. In real-world deployments, forgetting 'no shutdown' under an address-family is a frequent cause of silent routing failures, especially when migrating from classic to named EIGRP mode.
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 segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
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 EIGRP address-family is not activated because 'no shutdown' is missing under the address-family configuration. — The EIGRP address-family configuration for VRF RED is missing the 'no shutdown' command under the address-family mode. In Cisco IOS, EIGRP address-families are administratively shut down by default; without 'no shutdown', the EIGRP process for that VRF will not form adjacencies or advertise routes, even though the network command is correctly configured.
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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