- A
60 seconds
Why wrong: This is too short for general UDP traffic; RFC 4787 recommends 5 minutes.
- B
300 seconds
Correct. RFC 4787 recommends and Cisco IOS defaults to 300 seconds for UDP NAT mappings.
- C
600 seconds
Why wrong: This is not the recommended default; 300 seconds is the standard.
- D
86400 seconds
Why wrong: This is the default for basic NAT, not UDP mappings.
Question 941 of 2,152
UDP NAT Timeout — Default 300 Seconds per RFC 4787 | Cisco CCNP ENARSI 300-410 Explained
This 300-410 practice question tests your understanding of nat and pat. 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.
According to RFC 4787 (NAT Behavioral Requirements for UDP), what is the recommended default timeout for UDP NAT mappings?
Quick Answer
The answer is 300 seconds, or five minutes, as the recommended default UDP NAT timeout per RFC 4787. This standard, titled "Network Address Translation (NAT) Behavioral Requirements for UDP," establishes that a UDP mapping should remain active for at least five minutes after the last packet is seen to balance application responsiveness with efficient port utilization. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of NAT stateful behavior and the difference between UDP and TCP timeouts—a common trap is confusing the UDP default with TCP's longer default or assuming the timeout is indefinite. Cisco IOS routers honor this RFC by default, so you may see show ip nat translations output reflecting entries aged at 300 seconds. For a quick memory tip, think "UDP is quick, so five minutes is thick"—the short, connectionless nature of UDP still needs a generous timeout to handle DNS and VoIP traffic without premature drops.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
300 seconds
RFC 4787, Section 4.3, specifies that the recommended default timeout for UDP NAT mappings is 300 seconds (5 minutes). This value balances the need to maintain active sessions while promptly releasing stale mappings to conserve NAT table resources. Cisco IOS NAT implementations adhere to this recommendation by default for UDP translations.
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.
- ✗
60 seconds
Why it's wrong here
This is too short for general UDP traffic; RFC 4787 recommends 5 minutes.
- ✓
300 seconds
- ✗
600 seconds
Why it's wrong here
This is not the recommended default; 300 seconds is the standard.
- ✗
86400 seconds
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the UDP NAT timeout with the TCP NAT timeout (which defaults to 86400 seconds or 24 hours for established TCP sessions) or assume a shorter value like 60 seconds based on common application timeouts, rather than recalling the specific RFC 4787 recommendation.
Detailed technical explanation
How to think about this question
Under the hood, the NAT device maintains a mapping (inside local IP:port to outside global IP:port) and resets a timer each time a packet matches the mapping. RFC 4787 recommends a minimum of 2 minutes and a default of 5 minutes for UDP, but some implementations allow configuration via 'ip nat translation udp-timeout' in Cisco IOS. In real-world scenarios, misconfigured timeouts can cause issues with SIP/RTP media streams or long-lived DNS responses, where the default 300 seconds ensures sessions survive brief idle periods.
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 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.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this 300-410 question test?
NAT and PAT — This question tests NAT and PAT — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 300 seconds — RFC 4787, Section 4.3, specifies that the recommended default timeout for UDP NAT mappings is 300 seconds (5 minutes). This value balances the need to maintain active sessions while promptly releasing stale mappings to conserve NAT table resources. Cisco IOS NAT implementations adhere to this recommendation by default for UDP translations.
What should I do if I get this 300-410 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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Last reviewed: Jul 4, 2026
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