The answer is that the EPG and the L3Out are in different VRFs. In Cisco ACI, a contract provides policy-based connectivity, but it operates strictly within a single VRF boundary; the VRF defines the routing and policy enforcement domain. If the EPG and the Layer 3 Outside belong to different VRFs, the contract cannot be applied across them, so even if HTTP traffic is explicitly permitted, it will fail because the two constructs are isolated from each other. This scenario is a classic trap on the Cisco DCCOR / CCNP Data Center Core 350-601 exam, testing your understanding that VRF alignment is a prerequisite for any EPG-to-external network communication, regardless of contract rules. Many candidates mistakenly focus on contract direction or filter issues, but the root cause is almost always a VRF mismatch when an EPG to L3Out communication fails. Remember the memory tip: "No VRF, no contract—same VRF, same path."
350-601 Security Practice Question
This 350-601 practice question tests your understanding of security. 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.
In an ACI fabric, an EPG is configured with a contract that allows HTTP traffic to an external network. The external network is reachable via a Layer 3 Outside. However, HTTP traffic from the EPG fails. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The L3Out and the EPG are in different VRFs
Option B is correct because in Cisco ACI, communication between an EPG and an external network via a Layer 3 Outside requires both to be in the same VRF. If the EPG and the L3Out are in different VRFs, the contract cannot be enforced, and traffic will fail even if the contract allows HTTP. The VRF provides the routing and policy enforcement boundary for the contract.
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 subject action is set to deny
Why it's wrong here
If the subject action were deny, no external HTTP would be allowed.
✓
The L3Out and the EPG are in different VRFs
Why this is correct
ACI contracts only work within the same VRF. If the L3Out is in a different VRF, route leaking is required.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The filter uses the wrong direction
Why it's wrong here
Direction settings in filters affect which endpoints can initiate, but the HTTP filter should be bidirectional or set correctly.
✗
The contract is applied to the consumer EPG instead of the provider
Why it's wrong here
HTTP traffic originates from the EPG (consumer) to the external network (provider). The contract must be applied appropriately.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a contract alone is sufficient for inter-VRF communication, but in ACI, contracts are VRF-scoped and cannot bridge different VRFs without additional configuration like a VRF route leak or a shared service contract.
Detailed technical explanation
How to think about this question
In ACI, the VRF (also known as a Private Network) isolates routing and policy domains. A contract between an EPG and an L3Out is only effective when both endpoints reside in the same VRF; otherwise, the policy is not applied because the contract is scoped to the VRF. This is enforced by the ACI fabric's policy resolution mechanism, which checks VRF membership before installing contract rules in the hardware tables.
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
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.
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The L3Out and the EPG are in different VRFs — Option B is correct because in Cisco ACI, communication between an EPG and an external network via a Layer 3 Outside requires both to be in the same VRF. If the EPG and the L3Out are in different VRFs, the contract cannot be enforced, and traffic will fail even if the contract allows HTTP. The VRF provides the routing and policy enforcement boundary for the contract.
What should I do if I get this 350-601 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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