The answer is the Tenant construct. In Cisco ACI, a Tenant is the top-level logical container that enforces administrative and policy isolation, meaning that by default, no traffic flows between endpoints in different tenants because each Tenant operates as its own separate policy domain with no contracts or shared policies. On the ENCOR 350-401 exam, this concept tests your understanding of ACI’s fundamental segmentation model—a common trap is confusing Tenants with VRFs or Bridge Domains, which handle routing and forwarding but not policy isolation. The key distinction is that Tenant isolation is policy-driven, not IP-based; even if two endpoints in different Tenants share the same IP subnet, traffic is still blocked. A helpful memory tip: think of a Tenant as a locked apartment building—each tenant has their own key and no one can enter another’s unit without an explicit contract.
350-401 Enterprise Network Design Practice Question
This 350-401 practice question tests your understanding of enterprise network design. 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 network engineer is designing a data center network using Cisco ACI. The design must support multiple tenants with isolated policies. The engineer needs to ensure that traffic between endpoints in different tenants is blocked by default. Which ACI construct provides this isolation?
Correct because tenants in ACI provide administrative and policy isolation; endpoints in different tenants cannot communicate unless a contract is created between them.
B
VRF
Why wrong: Incorrect because VRFs provide Layer 3 isolation within a tenant, but they do not isolate traffic between tenants; tenants are the top-level isolation boundary.
C
Bridge Domain
Why wrong: Incorrect because bridge domains define Layer 2 boundaries within a tenant, not inter-tenant isolation.
D
Contract
Why wrong: Incorrect because contracts define policies that allow traffic; they are used to permit communication, not to block it by default.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Tenant
In Cisco ACI, a Tenant is the top-level logical container that provides administrative and policy isolation. By default, endpoints in different tenants cannot communicate because each tenant has its own separate policy domain, and no contracts exist between them. This makes the Tenant the correct construct for ensuring traffic between different tenants is blocked by default.
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.
✓
Tenant
Why this is correct
Correct because tenants in ACI provide administrative and policy isolation; endpoints in different tenants cannot communicate unless a contract is created between them.
Related concept
Read the scenario before looking for a memorised answer.
✗
VRF
Why it's wrong here
Incorrect because VRFs provide Layer 3 isolation within a tenant, but they do not isolate traffic between tenants; tenants are the top-level isolation boundary.
✗
Bridge Domain
Why it's wrong here
Incorrect because bridge domains define Layer 2 boundaries within a tenant, not inter-tenant isolation.
✗
Contract
Why it's wrong here
Incorrect because contracts define policies that allow traffic; they are used to permit communication, not to block it by default.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that VRFs or Bridge Domains provide cross-tenant isolation, but the trap here is that VRFs and BDs are scoped within a single tenant and do not inherently block traffic between different tenants—only the Tenant construct enforces default isolation.
Detailed technical explanation
How to think about this question
Under the hood, each ACI Tenant maps to a separate management and policy domain, with its own unique tenant ID used in the fabric's policy resolution. When no contracts are configured between tenants, the ACI fabric's default behavior is to drop all inter-tenant traffic at the leaf switch level, as the policy enforcement point (PEP) checks the tenant context before applying any forwarding decisions. In real-world multi-tenant data centers, this ensures that a tenant's VRF, BD, and EPG configurations remain completely isolated unless an administrator explicitly deploys a contract to allow cross-tenant communication.
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 practitioner preparing for the 350-401 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
Enterprise Network Design — This question tests Enterprise Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Tenant — In Cisco ACI, a Tenant is the top-level logical container that provides administrative and policy isolation. By default, endpoints in different tenants cannot communicate because each tenant has its own separate policy domain, and no contracts exist between them. This makes the Tenant the correct construct for ensuring traffic between different tenants is blocked by default.
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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