The answer is a contract between the EPGs. In Cisco ACI, inter-EPG communication within the same VRF is implicitly denied by default, regardless of whether unicast routing is enabled on the bridge domain. A contract is the only mechanism that explicitly permits traffic between EPGs by defining the subjects, filters, and actions (allow/deny) for that communication; without it, the fabric drops all packets between the EPGs. This concept is a frequent trap on the Cisco DCCOR 350-601 exam, where candidates often assume that enabling unicast routing alone opens inter-EPG traffic, but ACI’s zero-trust model requires a contract for any cross-EPG flow. A strong memory tip: think of EPGs as separate security zones—no contract means no conversation, even if they share the same VRF.
350-601 Network Practice Question
This 350-601 practice question tests your understanding of network. 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 a Cisco ACI fabric, a new EPG is created and associated with a bridge domain that has 'Unicast Routing' enabled. However, endpoints in that EPG cannot communicate with endpoints in other EPGs in the same VRF. What is missing?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A contract between the EPGs
In Cisco ACI, communication between EPGs within the same VRF is not allowed by default; it requires a contract. A contract defines the policies (allow/deny) and filters for traffic between EPGs. Without a contract, all traffic is dropped, even if the bridge domain has unicast routing enabled. Option C is correct because the missing element is the contract that explicitly permits inter-EPG communication.
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 EPG must be attached to a Layer 3 outside
Why it's wrong here
L3out is for external connectivity, not for internal EPG communication.
✗
The bridge domain must have 'L3 Unknown Multicast Flooding' set
Why it's wrong here
This setting affects multicast handling, not unicast inter-EPG communication.
✓
A contract between the EPGs
Why this is correct
Inter-EPG communication requires a contract; without it, packets are dropped.
Related concept
Read the scenario before looking for a memorised answer.
✗
A route leak between bridge domains
Why it's wrong here
Bridge domains in the same VRF can route to each other if unicast routing is enabled; no explicit leak needed.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that enabling unicast routing on a bridge domain is sufficient for inter-EPG communication, when in fact contracts are mandatory in ACI to allow any traffic between EPGs.
Detailed technical explanation
How to think about this question
ACI uses a policy-based architecture where contracts act as the firewall rules between EPGs. Even with unicast routing enabled on the bridge domain, the fabric's endpoint database (Endpoint Manager) will not forward packets between EPGs unless a contract is in place. In a real-world scenario, a common mistake is to assume that placing EPGs in the same VRF and bridge domain automatically allows communication, but ACI enforces zero-trust by default, requiring contracts for any cross-EPG traffic.
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.
Network — This question tests Network — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: A contract between the EPGs — In Cisco ACI, communication between EPGs within the same VRF is not allowed by default; it requires a contract. A contract defines the policies (allow/deny) and filters for traffic between EPGs. Without a contract, all traffic is dropped, even if the bridge domain has unicast routing enabled. Option C is correct because the missing element is the contract that explicitly permits inter-EPG communication.
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.
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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