Quick Answer
The answer is a subject that defines the filter. In Cisco ACI, a contract requires both a subject and a filter because the filter specifies the exact traffic parameters—such as IP protocol, source and destination ports, or EtherType—that are permitted or denied between EPGs, while the subject binds that filter to the contract and dictates the direction of traffic flow, either consumer-to-provider or bidirectional. Without both components, the contract lacks the criteria to match traffic and cannot allow communication. On the Cisco DCCOR 350-601 exam, this concept often appears as a trick where candidates mistakenly think a contract alone is sufficient, but the exam tests your understanding that the filter defines the rules and the subject applies them. A common memory tip is to think of the subject as the "glue" that attaches the filter to the contract, ensuring the filter’s rules are enforced in the correct direction.
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.
Which TWO of the following are required components for a Cisco ACI contract to allow communication between EPGs?
A filter that specifies the traffic parameters.
Filter defines allowed traffic.
A subject that defines the filter.
The subject links the contract to a filter.
A tenant.
Why wrong: Tenant is a container, not a direct component of a contract.
A QoS class.
Why wrong: QoS is optional.
A VRF.
Why wrong: VRF is for reachability, not part of contract.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
A filter that specifies the traffic parameters.
Option A is correct because a filter in Cisco ACI defines the specific traffic parameters—such as IP protocol, source/destination ports, and EtherType—that are permitted or denied between EPGs. Without a filter, the contract has no criteria to match traffic, so communication cannot be allowed. Option B is correct because a subject binds one or more filters to a contract and specifies the direction (consumer-to-provider or bidirectional) in which the filter is applied, making it an essential component for the contract to function.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
A filter that specifies the traffic parameters.
Why this is correct
Filter defines allowed traffic.
Related concept
Read the scenario before looking for a memorised answer.
A subject that defines the filter.
Why this is correct
The subject links the contract to a filter.
Related concept
Read the scenario before looking for a memorised answer.
A tenant.
Why it's wrong here
Tenant is a container, not a direct component of a contract.
A QoS class.
Why it's wrong here
QoS is optional.
A VRF.
Why it's wrong here
VRF is for reachability, not part of contract.
Common exam traps
Cisco often tests the misconception that a tenant or VRF is a required component of a contract, when in fact the contract only requires a filter and a subject to define the traffic rules, while tenants and VRFs are separate constructs that provide logical isolation and routing context.
Detailed technical explanation
In Cisco ACI, a contract is a policy construct that uses a subject to reference one or more filters, where each filter contains entries with parameters like IP protocol (e.g., tcp, udp, icmp), source/destination port ranges, and EtherType (e.g., 0x0800 for IPv4). The subject also defines the relationship direction (provider-to-consumer or bidirectional) and can include optional attributes like QoS class or target DSCP. Under the hood, the APIC translates these contract policies into hardware TCAM entries on the leaf switches, enabling or denying traffic flows between EPG endpoints based on the filter criteria.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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FAQ
Security — This question tests Security — Read the scenario before looking for a memorised answer..
The correct answer is: A filter that specifies the traffic parameters. — Option A is correct because a filter in Cisco ACI defines the specific traffic parameters—such as IP protocol, source/destination ports, and EtherType—that are permitted or denied between EPGs. Without a filter, the contract has no criteria to match traffic, so communication cannot be allowed. Option B is correct because a subject binds one or more filters to a contract and specifies the direction (consumer-to-provider or bidirectional) in which the filter is applied, making it an essential component for the contract to function.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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