Quick Answer
The answer is the source IP address, as it is a mandatory field in any Flexible NetFlow flow record for IPv4 traffic. This is because Flexible NetFlow requires at least one key field to define a unique flow, and the source IP address serves as the fundamental identifier for the originating host; without it, the flow record cannot distinguish one conversation from another. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of flow record configuration under the `flow record` command, where you must specify at least one `match` field—commonly the source IP address—while optional fields like destination port or protocol are added only for granularity. A common trap is assuming that destination port is mandatory for TCP/UDP flows, but the exam emphasizes that IPv4 flow records always require the source IP address as the baseline key. Memory tip: think of the source IP as the “who” in the conversation—without knowing who sent the packet, you cannot build a flow.
This 300-410 practice question tests your understanding of netflow and flexible netflow. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 of the following is a mandatory field in a Flexible NetFlow flow record for IPv4 traffic?
Destination port
Why wrong: Destination port is optional; it can be omitted.
Protocol type
Why wrong: Protocol type is optional; flows can be defined without it.
Source IP address
Correct. The source IP address is mandatory for IPv4 flow records.
TCP flags
Why wrong: TCP flags are optional and not mandatory.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Source IP address
The source IP address is a mandatory field in any IPv4 flow record; other fields like destination port are optional.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Destination port
Why it's wrong here
Destination port is optional; it can be omitted.
Protocol type
Why it's wrong here
Protocol type is optional; flows can be defined without it.
Source IP address
Why this is correct
Correct. The source IP address is mandatory for IPv4 flow records.
Related concept
Static NAT maps one inside address to one outside address.
TCP flags
Why it's wrong here
TCP flags are optional and not mandatory.
Common exam traps
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
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FAQ
NetFlow and Flexible NetFlow — This question tests NetFlow and Flexible NetFlow — Static NAT maps one inside address to one outside address..
The correct answer is: Source IP address — The source IP address is a mandatory field in any IPv4 flow record; other fields like destination port are optional.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 19, 2026
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.
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